- Use MD5 hashing for image and Spotify cache keys instead of raw hex
encoding (rpc.go) and SHA-256 (spotify.go)
- Validate Spotify track IDs with base-62 regex before using in URLs
- Fix buildSpotifySearchURL parameter order to match (artist, title) usage
- Tighten test mock matchers with shared helpers for cache keys and
external-assets URLs, replacing broad mock.Anything usage
- Update test Spotify IDs to use valid base-62 identifiers