feat: write unit tests for filtering logic

CLAUDE.md

@@ -152,6 +152,15 @@ Based on the specification (docs/Specification.md), the application follows a mo
 - Apply the specified fuzzy matching algorithm consistently
 - Centralize shared logic: Place reusable filtering, validation, or utility functions in dedicated files (e.g., internal/musicbrainz/filter.go) and import them across packages to ensure consistent behavior across cache-hit, cache-miss, and real-time paths
 
+### Execution Flow
+The application follows a sequential data pipeline:
+1. Sync artists from Navidrome (populate artist_settings)
+2. Sync discographies from MusicBrainz (populate external_releases with filtering)
+3. Sync albums from Navidrome (populate local_albums)
+4. Scan for missing releases using fuzzy matching (produces MissingRelease results)
+
+This flow is implemented in the `syncAndScan()` function in `cmd/naviwatcher/main.go`, which is called by the periodic sync loop and on startup.
+
 ## Configuration Reference
 See docs/Specification.md Section 7 for full config.yaml structure including:
 - Server settings (host, port, basic auth)