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/mpv.test.ts

@@ -387,6 +387,7 @@ test('buildRuntimeExtraScriptOptParts marks launcher-owned startup pause gate',
         autoStart: true,
         autoStartVisibleOverlay: true,
         autoStartPauseUntilReady: true,
+        osdMessages: false,
         texthookerEnabled: false,
         aniskipEnabled: true,
         aniskipButtonKey: 'TAB',
@@ -405,6 +406,7 @@ test('shouldResolveAniSkipMetadataForLaunch respects disabled runtime plugin Ani
       autoStart: true,
       autoStartVisibleOverlay: true,
       autoStartPauseUntilReady: true,
+      osdMessages: false,
       texthookerEnabled: false,
       aniskipEnabled: false,
       aniskipButtonKey: 'TAB',