refactor(launcher): split history.ts into focused modules

- Extract types → history-types.ts, DB layer → history-db.ts, navigation → history-navigation.ts
- history.ts becomes a re-export barrel
- Fix findNextEpisode: deleted-file fallback now advances to next season
- Add isReadonlyWalRetryError (WAL-mode guard before read-write retry)
- Strengthen bun-sqlite.d.ts with generics on Statement/query/prepare

launcher/history-types.ts

@@ -0,0 +1,21 @@
+export interface HistoryVideoRow {
+  videoId: number;
+  sourcePath: string;
+  parsedTitle: string | null;
+  parsedSeason: number | null;
+  parsedEpisode: number | null;
+  animeTitle: string | null;
+  lastWatchedMs: number;
+}
+
+export interface HistorySeriesEntry {
+  seriesRoot: string;
+  displayName: string;
+  lastWatched: HistoryVideoRow;
+}
+
+export interface SeasonDirEntry {
+  name: string;
+  path: string;
+  season: number | null;
+}