refactor: split Webcam out of MainViewModel — Commit 5/12 (tag refactor-commit-5)

ViewModels/index.md

@@ -50,12 +50,19 @@ Progress (Commit N/12 · tag):
   `ChangeCaptureCommand`/`RefreshCaptureCommand`/`SetBackgroundDisplayCommand`/
   `ToggleShowDesktopCommand`/`BrowseBackgroundCommand`). `ShowPreviewPlaceholder`
   stays in core.
+- **Commit 5/12 · `refactor-commit-5`: Webcam landed** → `MainViewModel.Webcam.cs`
+  (webcam identity `_webcam`/`ReacquireWebcam`/`SwapWebcamIdentityAsync`, per-scene
+  configs `AddWebcamToStagedSceneAsync`/`ShowWebcamInStagedScene`, capture lifetime
+  `OnCameraPreviewBitmapChanged`/`OnCameraFailed`, gating `CanAddWebcam`/
+  `CanChangeWebcam`/`CanShowWebcamInStagedScene`/`IsWebcamSelected`/`WebcamError`,
+  size safeguard `WebcamMax*`/`ClampWebcamToBounds`/`HealLegacySquareRect`,
+  `AddWebcamCommand`/`ChangeWebcamCommand`/`ShowWebcamCommand`).
 
 - Core file keeps: fields, ctor, `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`,
   `SetPanel`/`ShowOverlay`/`ShowLicenses`, `CreateBrush`, `OpenUrl`/`ComposeEmail`,
   `SubmitBug`/`SubmitFeature`, window-geometry pass-through.
 - Partials: `Account` ✔ (Commit 1), `License` ✔ (Commit 2), `Scenes` ✔ (Commit 3), `Background` ✔ (Commit 4),
-  `Webcam` (webcam identity + per-scene configs + captures),
+  `Webcam` ✔ (Commit 5),
   `Audio` (mic + game bars + TRAX), `Trax` (music player), `Socials` (social bar + dialog),
   `Streaming` (go-live/record + health + quality tiers + media source pipeline),
   `Chat` (YouTube chat + mock preview + chatbox render), `Overlays` (settings/bug/feature/about