Improve startup dictionary sync UX and default playback keybindings

- Add default `f` fullscreen overlay binding and switch default AniSkip skip key to `Tab`
- Make character-dictionary auto-sync non-blocking at startup with tokenization gating for Yomitan mutations
- Add ordered startup OSD progress (checking/generating/updating/importing), refresh current subtitle on sync completion, and extend regression tests

src/main/runtime/character-dictionary-auto-sync-notifications.ts

@@ -0,0 +1,34 @@
+import type { CharacterDictionaryAutoSyncStatusEvent } from './character-dictionary-auto-sync';
+import type { StartupOsdSequencerCharacterDictionaryEvent } from './startup-osd-sequencer';
+
+export type CharacterDictionaryAutoSyncNotificationEvent = CharacterDictionaryAutoSyncStatusEvent;
+
+export interface CharacterDictionaryAutoSyncNotificationDeps {
+  getNotificationType: () => 'osd' | 'system' | 'both' | 'none' | undefined;
+  showOsd: (message: string) => void;
+  showDesktopNotification: (title: string, options: { body?: string }) => void;
+  startupOsdSequencer?: {
+    notifyCharacterDictionaryStatus: (event: StartupOsdSequencerCharacterDictionaryEvent) => void;
+  };
+}
+
+function shouldShowOsd(type: 'osd' | 'system' | 'both' | 'none' | undefined): boolean {
+  return type !== 'none';
+}
+
+export function notifyCharacterDictionaryAutoSyncStatus(
+  event: CharacterDictionaryAutoSyncNotificationEvent,
+  deps: CharacterDictionaryAutoSyncNotificationDeps,
+): void {
+  const type = deps.getNotificationType();
+  if (shouldShowOsd(type)) {
+    if (deps.startupOsdSequencer) {
+      deps.startupOsdSequencer.notifyCharacterDictionaryStatus({
+        phase: event.phase,
+        message: event.message,
+      });
+      return;
+    }
+    deps.showOsd(event.message);
+  }
+}