Maintain macOS (showcase + native intentcall)

Dogfood app: flutter_test_app. Platform doc: flutter_test_app/INTENTCALL_PLATFORM.md.

WebMCP on macOS

WebMCP modelContext is web-only. macOS dogfood proves VM extensions, dynamic registry, native invoke (intentcall:// via app_links), and visual capture (Screen Recording on host).

For WebMCP parity scoring, run web iteration separately (flutter-mcp-toolkit-maintain-web).

Launch showcase

make showcase-stop && make showcase