refactor: split Scenes out of MainViewModel — Commit 3/12 (tag refactor-commit-3)

ViewModels/index.md

@@ -31,11 +31,18 @@ Progress (Commit N/12 · tag):
   (Polar license state: `LicenseKey`/`LicenseMessage`/`IsLicenseValidating`/
   `IsLicenseEntryOpen`/`IsHubVisible`/`IsPremium`, `OfflineGracePeriod`,
   `ValidateLicenseAtStartupAsync`, `ActivateLicenseAsync`).
+- **Commit 3/12 · `refactor-commit-3`: Scenes landed** → `MainViewModel.Scenes.cs`
+  (`Scenes` + `StagedScene`/`LiveScene`/`IsEditMode`, transitions
+  `SelectedTransitionType`/`TransitionDurationMs`/`TransitionToScene`/
+  `ApplyTransitionToLive`, global hotkeys `HandleHotkey`/`OpenHotkeyConfig`/
+  `RefreshHotkeyLabels`, scene-gating hints, `MissingScenes`/`ShowAddScene`/
+  `CanChangeBackground`, scene wiring `OnScenesChanged`/`WireScene`/`UnwireScene`,
+  `AddScene`).
 
 - 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` (scene catalog + hotkeys + transitions), `Background` (background model + screen
+- Partials: `Account` ✔ (Commit 1), `License` ✔ (Commit 2), `Scenes` ✔ (Commit 3), `Background` (background model + screen
   capture + display picker), `Webcam` (webcam identity + per-scene configs + captures),
   `Audio` (mic + game bars + TRAX), `Trax` (music player), `Socials` (social bar + dialog),
   `Streaming` (go-live/record + health + quality tiers + media source pipeline),