Add NAVIDROME_URL autofill, remove Navidrome scan trigger

- Frontend reads window.NS_SERVER_URL from config.js (injected at container start via docker-entrypoint.sh) and pre-fills the setup screen
- Removed triggerNaviScan from frontend and backend (Navidrome auto-scans on file change)
- Removed NAVIDROME_USER/PASS from backend and compose

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -1,11 +1,11 @@
 # Copy to .env and fill in your values
 
+# Pre-fills the server URL on the setup screen
+NAVIDROME_URL=https://music.yourdomain.com
+
+# Path to your Navidrome music library on the host
 MUSIC_PATH=/path/to/your/navidrome/music
 
 AUDIO_FMT=mp3          # mp3 | flac | opus | best
 AUDIO_QUALITY=0        # 0 = best quality
 MAX_PARALLEL=2
-
-NAVIDROME_URL=http://navidrome:4533
-NAVIDROME_USER=admin
-NAVIDROME_PASS=yourpassword