Add comprehensive test suite with CI workflow

- 211 tests across 15 files covering services (tracking, discovery,
  metadata, backup, credits, webhooks, settings, update-check, colors,
  person), utilities (config, cron, providers, title-theme), and TMDB
  image URL helpers
- `lib/test-preload.ts` + `bunfig.toml` wire up a global in-memory
  SQLite DB with migrations for all DB-backed tests
- `lib/test-utils.ts` provides `clearAllTables()` and seed helpers
  (insertUser, insertTitle, insertTvShow, insertMovieWatch, etc.)
- Export `getBackupSource`, `isKnownBackup`, `isValidBackupFilename`,
  `buildBackupCron`, `performUpdateCheck` internals for direct testing
- GitHub Actions workflow runs `bun test --coverage` on push/PR to main

lib/services/webhooks.ts

@@ -29,7 +29,8 @@ export interface WebhookEvent {
   showTitle?: string;
 }
 
-function toOptionalInt(value: unknown): number | undefined {
+/** @internal */
+export function toOptionalInt(value: unknown): number | undefined {
   if (typeof value === "number" && Number.isInteger(value)) {
     return value;
   }