fix: use npm install instead of npm ci, change port to 3091

- npm ci requires a package-lock.json; use npm install --omit=dev instead
- Change all port references from 3001 to 3091 (3001 is occupied)
  - docker-compose.yml: ports, PORT env, healthcheck URL
  - Dockerfile: EXPOSE
  - .env.example: PORT default

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

Dockerfile

@@ -5,13 +5,13 @@ RUN apk add --no-cache python3 make g++
 
 WORKDIR /app
 COPY package*.json ./
-RUN npm ci --omit=dev
+RUN npm install --omit=dev
 
 COPY . .
 
 RUN mkdir -p /data
 
-EXPOSE 3000
+EXPOSE 3091
 VOLUME ["/data"]
 
 CMD ["node", "server.js"]