Kill stringly-typed command tokens: Add Source menu passes SourceType enum via x:Static CommandParameter (typos break the build, not silently add an Image); webcam gets its own AddWebcamCommand; AddSource keeps Enum.TryParse fallback; docs updated (65 tests passing)

ai.md

@@ -95,7 +95,7 @@ C# / WPF (.NET 8) following MVVM:
 ### Key patterns
 
 - `ViewModelBase.SetProperty<T>()` for property change notifications
-- `RelayCommand` for all button actions; commands gate on state (e.g. Start only when Offline)
+- `RelayCommand` for all button actions; commands gate on state (e.g. Start only when Offline). **Typed `CommandParameter`s — no stringly-typed command tokens:** menu items that pick a source type pass the enum value itself (`CommandParameter="{x:Static models:SourceType.DisplayCapture}"`), so a typo breaks the build instead of silently adding an Image; `AddSource` still falls back to `Enum.TryParse<SourceType>(..., true)` for safety. The webcam item is its own `AddWebcamCommand` (it greys out via `CanAddWebcamToActiveScene` and isn't a `SourceType` — webcams are `WebcamSceneConfig`, not `Source` rows)
 - ViewModels are constructed in XAML (`<vm:MainViewModel/>` as DataContext)
 - Services are currently instantiated in MainViewModel's constructor — no DI container yet
 - Layout persists to SQLite (`Microsoft.Data.Sqlite`); scenes/sources/asset bytes stored in the DB, asset identity is a SHA-256 content hash (1:M reuse, no file paths — assets are always available)