cfg: d3d9 standalone configurator (#720)

## Description of change
**Configurator (spicecfg.exe)**

- Attempts to create a D3D9 device on startup and uses the hardware
ImGui DX9 path when successful; falls back to the existing software
rasterizer automatically if D3D9 init fails.
- Rewrites the configurator window loop: refresh-rate-aware render
timer, minimize/resize/`WM_DISPLAYCHANGE` handling, direct Win32 ->
ImGui input (keyboard, mouse, wheel), and optimized software painting
via `SetDIBitsToDevice` instead of per-frame GDI `HBITMAP` allocation.

**Overlay / input (scoped to standalone configurator)**

- Skips expensive per-frame rawinput polling in
`ImGui_ImplSpice_NewFrame` when `CONFIGURATOR_STANDALONE` is set (Win32
messages drive input instead).
- Adds software-renderer idle-frame detection (`sw_pixels_dirty` +
draw-data hash) so spicecfg only repaints when pixels actually change.
- Adds `ImGuiWindowFlags_NoScrollWithMouse` on the configurator root
window to prevent scroll jolt on non-scrollable child widgets.

src/spice2x/cfg/configurator_wnd.h

@@ -1,6 +1,9 @@
-#pragma once
+#pragma once
+
+#include <cstdint>
 
 #include <windows.h>
+#include <d3d9.h>
 
 namespace cfg {
 
@@ -9,11 +12,38 @@ namespace cfg {
 
         HWND hWnd;
 
+        // optional D3D9 device backing the configurator window; nullptr when running
+        // the software-rendered path. Owned by ConfiguratorWindow when set.
+        IDirect3D9 *d3d = nullptr;
+        IDirect3DDevice9 *device = nullptr;
+        D3DPRESENT_PARAMETERS pp {};
+        bool use_d3d9 = false;
+
+        // throttling / pause state. timer_interval_ms is the default until run()
+        // refines it to the actual monitor refresh rate (see detect_monitor_refresh_hz).
+        UINT timer_interval_ms = 1000 / 60;
+        bool timer_running = false;
+        bool window_minimized = false;
+
+        // tracks whether we've issued at least one InvalidateRect since window
+        // creation/resize. The overlay's per-frame "pixels changed" flag suppresses
+        // idle blits; this flag forces the very first blit on startup or after
+        // a resize so the window doesn't show garbage until the user moves the mouse.
+        bool has_valid_draw_hash = false;
+
+        // dimensions of the configurator client area (kept in sync with WM_SIZE)
+        int client_width = 0;
+        int client_height = 0;
+
         ConfiguratorWindow();
         ~ConfiguratorWindow();
 
         void run();
 
+        // start/stop the render timer based on visibility state
+        void start_timer();
+        void stop_timer();
+
         static LRESULT CALLBACK window_proc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
     };
 }