3.2: Code signing strategy (ad-hoc initial)

Sign the .app for Gatekeeper compatibility.

- [ ] Ad-hoc signing script: `codesign --deep --force --sign - "Path of Building 2.app"`
- [ ] Document first-launch workaround (right-click → Open) in user-facing README
- [ ] Track Apple Developer ID funding if the community wants full notarization

See MACOS_PORT.md §Phase 3 · 3.2