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'

README.md

@@ -38,6 +38,46 @@ docker-compose logs -f
 
 The proxy will be available at `http://localhost:5274`.
 
+## Web Dashboard
+
+Allstarr includes a web-based dashboard for easy configuration and playlist management, accessible at `http://localhost:5275` (internal port, not exposed through reverse proxy).
+
+### Features
+
+- **Real-time Status**: Monitor Spotify authentication, cookie age, and playlist sync status
+- **Playlist Management**: Link Jellyfin playlists to Spotify playlists with a few clicks
+- **Configuration Editor**: Update settings without manually editing .env files
+- **Track Viewer**: Browse tracks in your configured playlists
+- **Cache Management**: Clear cached data and restart the container
+
+### Quick Setup with Web UI
+
+1. **Access the dashboard** at `http://localhost:5275`
+2. **Configure Spotify** (Configuration tab):
+   - Enable Spotify API
+   - Add your `sp_dc` cookie from Spotify (see instructions in UI)
+   - The cookie age is automatically tracked
+3. **Link playlists** (Link Playlists tab):
+   - View all your Jellyfin playlists
+   - Click "Link to Spotify" on any playlist
+   - Paste the Spotify playlist ID, URL, or `spotify:playlist:` URI
+   - Accepts formats like:
+     - `37i9dQZF1DXcBWIGoYBM5M` (just the ID)
+     - `spotify:playlist:37i9dQZF1DXcBWIGoYBM5M` (Spotify URI)
+     - `https://open.spotify.com/playlist/37i9dQZF1DXcBWIGoYBM5M` (full URL)
+4. **Restart** to apply changes (button in Configuration tab)
+
+### Why Two Playlist Tabs?
+
+- **Link Playlists**: Shows all Jellyfin playlists and lets you connect them to Spotify
+- **Active Playlists**: Shows which Spotify playlists are currently being monitored and filled with tracks
+
+### Configuration Persistence
+
+The web UI updates your `.env` file directly. Changes persist across container restarts, but require a restart to take effect. In development mode, the `.env` file is in your project root. In Docker, it's at `/app/.env`.
+
+**Recommended workflow**: Use the `sp_dc` cookie method (simpler and more reliable than the Jellyfin Spotify Import plugin).
+
 ### Nginx Proxy Setup (Required)
 
 This service only exposes ports internally. You can use nginx to proxy to it, however PLEASE take significant precautions before exposing this! Everyone decides their own level of risk, but this is currently untested, potentially dangerous software, with almost unfettered access to your Jellyfin server. My recommendation is use Tailscale or something similar!