Add Docker setup: nginx frontend + backend compose

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

.env.example

@@ -0,0 +1,11 @@
+# Copy to .env and fill in your values
+
+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