refactor(notifications): extract routing predicates and fix pre-overlay

- Extract shouldShowOsd/Overlay/Desktop into notification-routing.ts (was duplicated in 3 files)
- Add resolveOverlayReadinessNotificationType: preserves system channel when overlay not ready (both→osd-system, system→system, overlay→osd)
- Route overlay loading status through showConfiguredStatusNotification instead of raw OSD

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

@@ -1,6 +1,7 @@
 import type { CharacterDictionaryAutoSyncStatusEvent } from './character-dictionary-auto-sync';
 import type { StartupOsdSequencerCharacterDictionaryEvent } from './startup-osd-sequencer';
 import type { NotificationType, OverlayNotificationPayload } from '../../types/notification';
+import { shouldShowDesktop, shouldShowOverlay, shouldShowOsd } from './notification-routing';
 
 export type CharacterDictionaryAutoSyncNotificationEvent = CharacterDictionaryAutoSyncStatusEvent;
 
@@ -16,18 +17,6 @@ export interface CharacterDictionaryAutoSyncNotificationDeps {
   };
 }
 
-function shouldShowOsd(type: NotificationType): boolean {
-  return type === 'osd' || type === 'osd-system';
-}
-
-function shouldShowOverlay(type: NotificationType): boolean {
-  return type === 'overlay' || type === 'both';
-}
-
-function shouldShowDesktop(type: NotificationType): boolean {
-  return type === 'system' || type === 'both' || type === 'osd-system';
-}
-
 function isTerminalPhase(phase: CharacterDictionaryAutoSyncNotificationEvent['phase']): boolean {
   return phase === 'ready' || phase === 'failed';
 }