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>

.env.example

@@ -1,4 +1,4 @@
-PORT=3001
+PORT=3091
 DB_PATH=/data/bots.db
 NODE_ENV=production
 # Set a strong random token — all WP sites must send this as: Authorization: Bearer <token>