feat: server-side romaji overrides (shared list); preload ExoPlayer from SharedPreferences on cold start

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

docker-compose.yml

@@ -20,11 +20,13 @@ services:
     volumes:
       - ./backend:/app:ro                # mount entire backend dir (server + lib/)
       - ${MUSIC_PATH}:${MUSIC_PATH}      # exact path from .env, no remapping
+      - novasonic-data:/data             # writable data dir for overrides, state, etc.
     ports:
       - "3700:3700"                      # route this port through your reverse proxy
     environment:
       - PORT=3700
       - MUSIC_PATH=${MUSIC_PATH}         # same path inside the container
+      - DATA_PATH=/data
       - AUDIO_FMT=${AUDIO_FMT:-mp3}
       - AUDIO_QUALITY=${AUDIO_QUALITY:-0}
       - MAX_PARALLEL=${MAX_PARALLEL:-2}
@@ -38,3 +40,6 @@ services:
         mkdir -p /deps && cd /deps && npm install express kuromoji &&
         cd /app && NODE_PATH=/deps/node_modules node novasonic-server.js
       "
+
+volumes:
+  novasonic-data:    # persistent storage for romaji overrides and app state