4.3: Mirror update-simple-graphic dispatch for macOS dylibs

[braggpd]

On SimpleGraphic release, auto-PR the macOS dylibs into braggpd/PathOfBuilding-PoE2 via a repository_dispatch event — mirroring the existing Windows DLL update workflow.

• Add macOS variant of update-simple-graphic.yml in PoB-PoE2 fork
• PR targets runtime-macos/ directory
• Tested end-to-end with a test release tag

See MACOS_PORT.md §Phase 4 · 4.3