fix: add kuromoji to backend container npm install

The backend uses NODE_PATH=/deps/node_modules with its own npm install
step — not the root package.json. Added kuromoji there and reverted
the incorrect root package.json change.

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

docker-compose.yml

@@ -35,6 +35,6 @@ services:
         apt-get update && apt-get install -y --no-install-recommends python3 python3-pip ffmpeg curl git && rm -rf /var/lib/apt/lists/* &&
         curl -sL https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp -o /usr/local/bin/yt-dlp && chmod a+rx /usr/local/bin/yt-dlp &&
         pip install --break-system-packages spotapi 'git+https://github.com/TzurSoffer/spotify-downloader' &&
-        mkdir -p /deps && cd /deps && npm install express &&
+        mkdir -p /deps && cd /deps && npm install express kuromoji &&
         cd /app && NODE_PATH=/deps/node_modules node novasonic-server.js
       "