feat(notifications): add overlay notifications with position config

- Add Catppuccin Macchiato overlay notification stack with 3s transient timeout
- Add `notifications.overlayPosition` config (top-left | top | top-right)
- Route startup tokenization and subtitle annotation status through configured surfaces
- Deduplicate rapid subtitle mode toggle notifications
- Change `both` to mean overlay + system; add `osd-system` as legacy alias for old behavior
- Keep `osd`/`osd-system` as config-file-only legacy values; Settings UI offers overlay/system/both/none

launcher/commands/command-modules.test.ts

@@ -45,6 +45,7 @@ function createContext(overrides: Partial<LauncherCommandContext> = {}): Launche
       autoStart: true,
       autoStartVisibleOverlay: true,
       autoStartPauseUntilReady: true,
+      osdMessages: false,
       texthookerEnabled: false,
       aniskipEnabled: true,
       aniskipButtonKey: 'TAB',