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>

docker-compose.yml

@@ -7,6 +7,8 @@ services:
     restart: unless-stopped
     ports:
       - "8080:80"          # route this port through your reverse proxy
+    environment:
+      - NAVIDROME_URL=${NAVIDROME_URL}   # pre-filled on the setup screen
 
   # ── Backend (yt-dlp download server) ─────────────────────────────────────────
   novasonic-backend:
@@ -25,9 +27,6 @@ services:
       - AUDIO_FMT=${AUDIO_FMT:-mp3}
       - AUDIO_QUALITY=${AUDIO_QUALITY:-0}
       - MAX_PARALLEL=${MAX_PARALLEL:-2}
-      - NAVIDROME_URL=${NAVIDROME_URL:-}
-      - NAVIDROME_USER=${NAVIDROME_USER:-}
-      - NAVIDROME_PASS=${NAVIDROME_PASS:-}
     command: >
       sh -c "
         apk add --no-cache yt-dlp ffmpeg python3 &&