fix(docker): add gateway subcommand and cloud-compatible flags

The Dockerfile CMD runs without arguments, causing the CLI to print
help and exit with code 1. This breaks deployment on container
platforms (Render, Railway, Fly.io, etc.) that rely on the CMD.

Changes:
- Add `gateway` subcommand to start the server
- Add `--allow-unconfigured` to allow startup without config file
- Add `--bind lan` to bind to 0.0.0.0 instead of localhost
  (required for container health checks)

Fixes #5685

Dockerfile

@@ -39,4 +39,4 @@ RUN chown -R node:node /app
 # This reduces the attack surface by preventing container escape via root privileges
 USER node
 
-CMD ["node", "dist/index.js"]
+CMD ["node", "dist/index.js", "gateway", "--allow-unconfigured", "--bind", "lan"]