feat(gemini): add Google Cloud Project support and improve error handling

- Add `happy gemini project set/get` commands for Workspace accounts
- Store project ID per-account (linked to email)
- Show helpful error message for "Authentication required" with guide link
- Sync local ~/.gemini/oauth_creds.json on `happy connect gemini`
- Add `happy connect status` command to show vendor auth status
- Pass GOOGLE_CLOUD_PROJECT env var to Gemini SDK