add desktop connector management

[pmbstyle]

Summary

• add a Desktop Connectors tab for Google and GitHub configuration, service toggles, auth, disconnect, and runtime status
• add a dashboard connector apply endpoint so a running instance can reload connector config and reconcile connector-backed MCP servers without restart
• harden Desktop connector JSON parsing for noisy command output

Validation

• npm run build (desktop)
• uv run pytest tests/test_dashboard_v2_api.py tests/test_connectors.py
• uv run ruff check src/octopal/gateway/dashboard.py tests/test_dashboard_v2_api.py