Prepare React + C++ desktop template for public release

[Koshkej]

Summary

• rebrand and document the template for an English-speaking open-source audience
• add native macOS menus/shortcuts, integrated window behavior, viewport defaults, and one-source cross-platform icons
• harden the typed C++/React bridge, generator metadata, dependencies, CI, and community files
• add a real generated-app preview and public-readiness tests

Validation

• python3 -m unittest discover -s tests -v
• generated frontend typecheck, Vitest, Vite production build, and contract verification
• generated macOS CMake build, CTest, runtime smoke test, native shortcuts, and CPack DMG
• Node reference implementation frontend/native build, CTest, runtime smoke test, and CPack DMG

Windows and Linux are validated by the GitHub Actions matrix.