feat(overlay): add loading OSD spinner and queue notifications until ren

- Show mpv OSD spinner from start-file until subminer-overlay-loading-ready; force-shown for visible-overlay startup regardless of osd_messages setting
- Gate non-macOS overlay visibility on content-ready so first subtitle line is immediately hoverable and clickable
- Queue startup notifications in main process until overlay window finishes loading; upsert progress cards by id to avoid cold-start floods
- Defer background warmups until after overlay runtime init so queued notifications can deliver promptly
- Preserve character dictionary checking/building/importing/ready phases as distinct history entries; route building and importing to system notifications when notificationType is both

src/main/runtime/overlay-window-factory-main-deps.ts

@@ -14,6 +14,7 @@ export function createBuildCreateOverlayWindowMainDepsHandler<TWindow>(deps: {
       linuxX11FullscreenOverlay?: boolean;
       onVisibleWindowBlurred?: () => void;
       onVisibleWindowFocused?: () => void;
+      onWindowDidFinishLoad?: () => void;
       onWindowContentReady?: () => void;
       onWindowClosed: (windowKind: 'visible' | 'modal', window: TWindow) => void;
       yomitanSession?: Session | null;
@@ -29,6 +30,7 @@ export function createBuildCreateOverlayWindowMainDepsHandler<TWindow>(deps: {
   getLinuxX11FullscreenOverlay?: () => boolean;
   onVisibleWindowBlurred?: () => void;
   onVisibleWindowFocused?: () => void;
+  onWindowDidFinishLoad?: () => void;
   onWindowContentReady?: () => void;
   onWindowClosed: (windowKind: 'visible' | 'modal', window: TWindow) => void;
   getYomitanSession?: () => Session | null;
@@ -45,6 +47,7 @@ export function createBuildCreateOverlayWindowMainDepsHandler<TWindow>(deps: {
     getLinuxX11FullscreenOverlay: deps.getLinuxX11FullscreenOverlay,
     onVisibleWindowBlurred: deps.onVisibleWindowBlurred,
     onVisibleWindowFocused: deps.onVisibleWindowFocused,
+    onWindowDidFinishLoad: deps.onWindowDidFinishLoad,
     onWindowContentReady: deps.onWindowContentReady,
     onWindowClosed: deps.onWindowClosed,
     getYomitanSession: () => deps.getYomitanSession?.() ?? null,