overlay: OBS control window via WebSocket API (#773)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Adds an overlay window widget for controlling OBS over WebSocket.

Add new lines to the FPS widget that shows recording / streaming timers.

Show notifications for major state changes (stream started/stopped,
recording started/paused/resumed/stopped)

## Testing

src/spice2x/overlay/windows/obs.cpp

@@ -0,0 +1,290 @@
+#include "obs.h"
+
+#include <algorithm>
+#include <chrono>
+#include <cstdio>
+
+#include "external/imgui/imgui.h"
+
+#include "games/io.h"
+#include "overlay/overlay.h"
+#include "overlay/imgui/extensions.h"
+
+using namespace std::chrono;
+
+// OBS WebSocket protocol/worker thread lives in obs_websocket.cpp; this file
+// owns the ImGui control window and the connection lifecycle.
+
+namespace {
+
+    // status text colors
+    const ImVec4 COL_GREEN(0.40f, 0.85f, 0.40f, 1.0f);
+    const ImVec4 COL_RED(0.90f, 0.30f, 0.30f, 1.0f);
+    const ImVec4 COL_YELLOW(0.95f, 0.80f, 0.30f, 1.0f);
+    const ImVec4 COL_GREY(0.60f, 0.60f, 0.60f, 1.0f);
+
+    // muted action-button fills (start = green, stop = red, pause = yellow); the
+    // hovered/active shades are derived by brightening the base
+    const ImVec4 COL_BTN_GREEN(0.20f, 0.45f, 0.24f, 1.0f);
+    const ImVec4 COL_BTN_RED(0.52f, 0.20f, 0.20f, 1.0f);
+    const ImVec4 COL_BTN_YELLOW(0.52f, 0.42f, 0.16f, 1.0f);
+
+    // an in-flight request lingers for at most this long before the button frees
+    // itself, so a dropped state event can never wedge a control permanently
+    const int64_t PENDING_TIMEOUT_MS = 5000;
+
+    int64_t now_tick_ms() {
+        return duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
+    }
+
+    std::string format_duration(int64_t ms) {
+        if (ms < 0) {
+            ms = 0;
+        }
+        const int64_t total_seconds = ms / 1000;
+        const int64_t hours = total_seconds / 3600;
+        const int64_t minutes = (total_seconds % 3600) / 60;
+        const int64_t seconds = total_seconds % 60;
+        char buf[16];
+        snprintf(buf, sizeof(buf), "%02lld:%02lld:%02lld",
+                 static_cast<long long>(hours),
+                 static_cast<long long>(minutes),
+                 static_cast<long long>(seconds));
+        return buf;
+    }
+}
+
+namespace overlay::windows {
+
+    OBSControl::OBSControl(SpiceOverlay *overlay) : Window(overlay) {
+        this->title = "OBS Control";
+        this->flags |= ImGuiWindowFlags_AlwaysAutoResize;
+        this->init_pos = overlay::apply_scaling_to_vector(120, 120);
+        this->toggle_button = games::OverlayButtons::ToggleOBSControl;
+
+        this->worker_running.store(true);
+        this->worker_thread = std::thread(&OBSControl::worker_main, this);
+    }
+
+    OBSControl::~OBSControl() {
+        // signal stop and wake any in-progress interruptible_sleep at once; the
+        // lock around the store pairs with the wait predicate to avoid a lost wakeup
+        {
+            std::lock_guard<std::mutex> lock(this->worker_mutex);
+            this->worker_running.store(false);
+        }
+        this->worker_cv.notify_all();
+        if (this->worker_thread.joinable()) {
+            // note: if the worker is mid-connect, WebSocket::from_url performs a
+            // blocking getaddrinfo/connect that does not observe worker_running,
+            // so this join can stall for the OS connect timeout. the default
+            // 127.0.0.1 host fails fast (connection refused); only a misconfigured
+            // unreachable remote OBS_CONTROL_HOST would delay shutdown here.
+            this->worker_thread.join();
+        }
+    }
+
+    OBSStatus OBSControl::get_status() {
+        std::lock_guard<std::mutex> lock(this->status_mutex);
+        return this->status;
+    }
+
+    int64_t OBSControl::live_duration_ms(int64_t base_ms, int64_t base_tick, bool ticking) {
+        if (!ticking) {
+            return (std::max<int64_t>)(base_ms, 0);
+        }
+        const int64_t now =
+            duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
+        // clamp so a stale base tick / clock hiccup can never yield a negative
+        // duration; callers (FPS rows, build_content) format this directly
+        return (std::max<int64_t>)(base_ms + (now - base_tick), 0);
+    }
+
+    void OBSControl::build_content() {
+
+        const OBSStatus s = this->get_status();
+
+        // label + colored value on a single line
+        const auto status_line = [](const char *label, const ImVec4 &col, const char *value) {
+            ImGui::Text("%s", label);
+            ImGui::SameLine();
+            ImGui::TextColored(col, "%s", value);
+        };
+
+        if (!s.connected) {
+            if (s.disabled) {
+                ImGui::TextColored(COL_GREY, "%s", "OBS Control is disabled");
+                return;
+            }
+            if (s.identifying) {
+                status_line("OBS WebSocket:", COL_YELLOW, "Connecting...");
+            } else {
+                status_line("OBS WebSocket:", COL_GREY, "Not connected");
+            }
+            const std::string url =
+                "ws://" + OBS_CONTROL_HOST + ":" + std::to_string(OBS_CONTROL_PORT);
+            status_line("Address:", COL_GREY, url.c_str());
+            if (!s.connection_error.empty()) {
+                ImGui::TextColored(COL_RED, "%s", s.connection_error.c_str());
+            }
+            return;
+        }
+
+        status_line("OBS WebSocket:", COL_GREEN, "Connected");
+
+        // one fixed content width drives the whole panel so it never resizes as
+        // the scene name or button labels change; every row is sized to fit it
+        const float spacing = ImGui::GetStyle().ItemSpacing.x;
+        const float row_w = overlay::apply_scaling(240);
+
+        if (s.current_scene.empty()) {
+            status_line("Scene:", COL_GREY, "(unknown)");
+        } else {
+            ImGui::Text("Scene:");
+            ImGui::SameLine();
+            // truncate to the remaining row width so "Scene:" + value together
+            // never overflow and push the window wider
+            const float label_w = ImGui::CalcTextSize("Scene:").x;
+            ImGui::PushStyleColor(ImGuiCol_Text, COL_GREY);
+            ImGui::TextTruncated(s.current_scene, row_w - label_w - spacing);
+            ImGui::PopStyleColor();
+        }
+
+        ImGui::Separator();
+
+        const int64_t now = now_tick_ms();
+        // every button shares one fixed size; two side-by-side fill the row width,
+        // single buttons keep that same size rather than stretching to fill
+        const ImVec2 btn((row_w - spacing) * 0.5f, 0);
+
+        // has OBS reached the state a pending action was waiting for?
+        const auto reached = [&](OBSAction a) {
+            switch (a) {
+                case OBSAction::StreamStart: return s.streaming;
+                case OBSAction::StreamStop: return !s.streaming;
+                case OBSAction::RecordStart: return s.recording;
+                case OBSAction::RecordStop: return !s.recording;
+                case OBSAction::RecordPause: return s.record_paused;
+                case OBSAction::RecordResume: return !s.record_paused;
+                default: return true;
+            }
+        };
+
+        // drop a pending action once OBS confirms the new state, or once the
+        // safety deadline lapses (so a dropped event can't wedge the button)
+        const auto settle = [&](OBSAction &slot, int64_t deadline) {
+            if (slot != OBSAction::None && (reached(slot) || now >= deadline)) {
+                slot = OBSAction::None;
+            }
+        };
+        settle(this->stream_pending, this->stream_pending_deadline);
+        settle(this->record_pending, this->record_pending_deadline);
+
+        // a colored button that fires a request and marks the output busy on click
+        const auto action_button =
+            [&](const char *label,
+                const ImVec4 &color,
+                const char *request,
+                OBSAction &slot,
+                int64_t &deadline,
+                OBSAction action) {
+
+            if (ImGui::ColoredButton(label, color, btn)) {
+                enqueue_request(request);
+                slot = action;
+                deadline = now + PENDING_TIMEOUT_MS;
+            }
+        };
+
+        // streaming
+        {
+            const bool pending = this->stream_pending != OBSAction::None;
+
+            if (s.streaming) {
+                const int64_t ms = live_duration_ms(
+                    s.stream_duration_ms, s.stream_duration_base_tick, true);
+                status_line("Streaming:", COL_RED, ("LIVE " + format_duration(ms)).c_str());
+            } else {
+                status_line("Streaming:", COL_GREY, pending ? "Starting..." : "Idle");
+            }
+
+            ImGui::BeginDisabled(pending);
+            if (s.streaming) {
+                action_button(
+                    pending ? "Stopping...##stream" : "Stop Streaming##stream",
+                    COL_BTN_RED,
+                    "StopStream",
+                    this->stream_pending,
+                    this->stream_pending_deadline,
+                    OBSAction::StreamStop);
+            } else {
+                action_button(
+                    pending ? "Starting...##stream" : "Start Streaming##stream",
+                    COL_BTN_GREEN,
+                    "StartStream",
+                    this->stream_pending,
+                    this->stream_pending_deadline,
+                    OBSAction::StreamStart);
+            }
+            ImGui::EndDisabled();
+        }
+
+        ImGui::Separator();
+
+        // recording
+        {
+            const bool pending = this->record_pending != OBSAction::None;
+
+            if (!s.recording) {
+                status_line("Recording:", COL_GREY, pending ? "Starting..." : "Idle");
+                ImGui::BeginDisabled(pending);
+                action_button(
+                    pending ? "Starting...##record" : "Start Recording##record",
+                    COL_BTN_GREEN,
+                    "StartRecord",
+                    this->record_pending,
+                    this->record_pending_deadline,
+                    OBSAction::RecordStart);
+                ImGui::EndDisabled();
+                return;
+            }
+
+            const int64_t ms = live_duration_ms(
+                s.record_duration_ms, s.record_duration_base_tick, !s.record_paused);
+            if (s.record_paused) {
+                status_line("Recording:", COL_YELLOW, ("PAUSED " + format_duration(ms)).c_str());
+            } else {
+                status_line("Recording:", COL_RED, ("REC " + format_duration(ms)).c_str());
+            }
+
+            ImGui::BeginDisabled(pending);
+            action_button(
+                this->record_pending == OBSAction::RecordStop ? "Stopping...##record" : "Stop Recording##record",
+                COL_BTN_RED,
+                "StopRecord",
+                this->record_pending,
+                this->record_pending_deadline, OBSAction::RecordStop);
+
+            ImGui::SameLine();
+            if (s.record_paused) {
+                action_button(
+                    this->record_pending == OBSAction::RecordResume ? "Resuming...##record_toggle" : "Resume##record_toggle",
+                    COL_BTN_GREEN,
+                    "ResumeRecord",
+                    this->record_pending,
+                    this->record_pending_deadline,
+                    OBSAction::RecordResume);
+
+            } else {
+                action_button(
+                    this->record_pending == OBSAction::RecordPause ? "Pausing...##record_toggle" : "Pause##record_toggle",
+                    COL_BTN_YELLOW,
+                    "PauseRecord",
+                    this->record_pending,
+                    this->record_pending_deadline,
+                    OBSAction::RecordPause);
+            }
+            ImGui::EndDisabled();
+        }
+    }
+}