refactor: remove sync window logic from Spotify Import

- Simplified SpotifyMissingTracksFetcher to remove complex sync window timing
- Now fetches on startup if cache missing, then checks every 5 minutes for stale cache (>24h)
- Removed SYNC_START_HOUR, SYNC_START_MINUTE, SYNC_WINDOW_HOURS from config
- Updated README and .env.example to reflect simpler configuration
- Sync window was only relevant for legacy Jellyfin plugin scraping method
- When using sp_dc cookie method (recommended), this service is dormant anyway
- Deleted MIGRATION.md (local-only file, not for repo)

README.md

@@ -360,9 +360,6 @@ Allstarr automatically fills your Spotify playlists (like Release Radar and Disc
 | Setting | Description |
 |---------|-------------|
 | `SpotifyImport:Enabled` | Enable Spotify playlist injection (default: `false`) |
-| `SpotifyImport:SyncStartHour` | Hour when plugin runs (24-hour format, 0-23) - used for sync window check |
-| `SpotifyImport:SyncStartMinute` | Minute when plugin runs (0-59) - used for sync window check |
-| `SpotifyImport:SyncWindowHours` | Hours to check for missing tracks files after sync time (default: 2) |
 | `SpotifyImport:MatchingIntervalHours` | How often to run track matching in hours (default: 24, set to 0 for startup only) |
 | `SpotifyImport:Playlists` | JSON array of playlists (managed via Web UI) |
 
@@ -371,11 +368,6 @@ Allstarr automatically fills your Spotify playlists (like Release Radar and Disc
 # Enable the feature
 SPOTIFY_IMPORT_ENABLED=true
 
-# Sync window settings (used to avoid fetching too frequently)
-SPOTIFY_IMPORT_SYNC_START_HOUR=16
-SPOTIFY_IMPORT_SYNC_START_MINUTE=15
-SPOTIFY_IMPORT_SYNC_WINDOW_HOURS=2
-
 # Matching interval (24 hours = once per day)
 SPOTIFY_IMPORT_MATCHING_INTERVAL_HOURS=24