🔧 update (cli): add --docker flag for container environments

Add container environment detection and --docker flag to route setup
to the web-based flow, preventing CLI prompts from hanging in
non-TTY container environments.

Changes:
- Add isRunningInContainer() in detect-container.ts (shared utility)
- Auto-detect Docker/CI via env vars, .dockerenv, and cgroup
- Add --docker flag as alias for --web in container contexts
- Show container warning in interactive setup with escape hatch
- Update help text with --docker documentation

Author: youhanasheriff