Add controller presets management (#581)

## Link to GitHub Issue or related Pull Request, if one exists
Implements #579.

## Description of change

### Controller Presets

Add a new "Presets" tab to spicecfg that allows users to save, load, and
manage controller binding presets.

#### Save Presets
- Capture all current button, analog, and light bindings as a preset
- "Assign Labels" dialog prompts the user to name each source device
(e.g. "Player 1", "Player 2") before saving
- Device IDs are replaced with these labels, making presets portable
across different machines
- Presets are stored in `%APPDATA%/spice2x/spicetools_presets.xml`

#### Load / Apply Presets
- Preset list shows name, type (Built-in / User), and binding counts
- Apply dialog maps each preset source label to a connected device or
keyboard
- Bindings are applied per-source, supporting multi-device setups (e.g.
two PHOENIXWAN controllers)

#### Edit / Delete Presets
- Rename source labels in saved presets (propagates to all bindings)
- Delete user presets

#### Built-in Presets
- PHOENIXWAN preset for Beatmania IIDX: P1/P2 buttons (1-7, Start,
EFFECT, VEFX), turntable analogs, and button lights

## Testing

* [x] Open spicecfg, go to Buttons tab, verify Presets section loads
* [x] Verify PHOENIXWAN builtin preset appears for Beatmania IIDX
* [x] Save a new preset: confirm "Assign Labels" dialog appears with
device descriptions as defaults
* [x] Apply a preset: confirm source column shows labels, popup does not
shrink
* [x] Edit labels on a saved preset: confirm rename propagates to all
bindings
* [x] Hover over a device source tooltip: confirm vKey shows as number

src/spice2x/cfg/button.h

@@ -63,10 +63,10 @@ private:
     float last_velocity = 0.f;
     unsigned short velocity_threshold = 0;
 
-    std::string getVKeyString();
     std::string getMidiNoteString();
 
 public:
+    std::string getVKeyString();
 
     // overrides
     bool override_enabled = false;