Fix web UI config persistence and cookie age tracking

- Add SPOTIFY_API_SESSION_COOKIE_SET_DATE to docker-compose.yml env mapping
- Mount .env file in container for web UI to update
- Add SessionCookieSetDate loading in Program.cs
- Improve .env update logic with better error handling and logging
- Auto-initialize cookie date when cookie exists but date not set
- Simplify local vs external track detection in Jellyfin playlists
- Enhanced Spotify playlist ID parsing (supports ID, URI, and URL formats)
- Better UI clarity: renamed tabs to 'Link Playlists' and 'Active Playlists'

docker-compose.yml

@@ -94,6 +94,7 @@ services:
       - SpotifyApi__ClientId=${SPOTIFY_API_CLIENT_ID:-}
       - SpotifyApi__ClientSecret=${SPOTIFY_API_CLIENT_SECRET:-}
       - SpotifyApi__SessionCookie=${SPOTIFY_API_SESSION_COOKIE:-}
+      - SpotifyApi__SessionCookieSetDate=${SPOTIFY_API_SESSION_COOKIE_SET_DATE:-}
       - SpotifyApi__CacheDurationMinutes=${SPOTIFY_API_CACHE_DURATION_MINUTES:-60}
       - SpotifyApi__RateLimitDelayMs=${SPOTIFY_API_RATE_LIMIT_DELAY_MS:-100}
       - SpotifyApi__PreferIsrcMatching=${SPOTIFY_API_PREFER_ISRC_MATCHING:-true}
@@ -111,6 +112,8 @@ services:
       - ${DOWNLOAD_PATH:-./downloads}:/app/downloads
       - ${KEPT_PATH:-./kept}:/app/kept
       - ${CACHE_PATH:-./cache}:/app/cache
+      # Mount .env file for runtime configuration updates from admin UI
+      - ./.env:/app/.env
       # Docker socket for self-restart capability (admin UI only)
       - /var/run/docker.sock:/var/run/docker.sock:ro