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

.github/workflows/test.yml

@@ -0,0 +1,28 @@
+name: Test
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+
+      - name: Install dependencies
+        run: bun install --frozen-lockfile
+
+      - name: Run tests with coverage
+        run: bun test --coverage --coverage-reporter=lcov
+
+      # - name: Upload to Codecov
+      #   uses: codecov/codecov-action@v3
+      #   with:
+      #     file: ./coverage/lcov.info
+      #     fail_ci_if_error: true