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

src/renderer/state.ts

@@ -31,6 +31,7 @@ export type ChordAction =
 export type RendererState = {
   isOverSubtitle: boolean;
   isOverSubtitleSidebar: boolean;
+  isOverOverlayNotification: boolean;
   isDragging: boolean;
   dragStartY: number;
   startYPercent: number;
@@ -143,6 +144,7 @@ export function createRendererState(): RendererState {
   return {
     isOverSubtitle: false,
     isOverSubtitleSidebar: false,
+    isOverOverlayNotification: false,
     isDragging: false,
     dragStartY: 0,
     startYPercent: 0,