Fix Docker build: lockfile, BuildKit DNS, and setuptools build backend

- Generate frontend/package-lock.json (required by npm ci)
- Add network: host to BuildKit build stages to fix DNS in pip installs
- Switch pyproject.toml build backend to setuptools.build_meta (stable)

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

docker-compose.yml

@@ -23,6 +23,7 @@ services:
     build:
       context: ./backend
       dockerfile: Dockerfile
+      network: host
     restart: unless-stopped
     env_file: ./backend/.env
     environment:
@@ -38,6 +39,7 @@ services:
     build:
       context: ./frontend
       dockerfile: Dockerfile
+      network: host
     restart: unless-stopped
     ports:
       - "80:80"