Promote C bridge out of frontend/macos/ into its own platform-agnostic component

[OldCrow]

Summary

The C bridge (ewcalc_bridge.h / ewcalc_bridge.cpp) lives under frontend/macos/bridge/ despite being entirely platform-agnostic. It is tested from ewpresenter/tests/, not from the macOS frontend tests. Its current location misleads contributors into thinking it is macOS-specific and discourages its use from other frontends.

Proposed structure

Move the bridge to a dedicated top-level component, e.g.:

ewpresenter/
├── bridge/
│   ├── ewcalc_bridge.h
│   ├── ewcalc_bridge.cpp
│   └── CMakeLists.txt

or

bridge/
├── ewcalc_bridge.h
├── ewcalc_bridge.cpp
└── CMakeLists.txt

Action needed

1. Move frontend/macos/bridge/ files to the new location.
2. Update CMakeLists.txt at the root and in ewpresenter/tests/ to reference the new path.
3. Update frontend/macos/CMakeLists.txt to link against the bridge at its new location.
4. Update frontend/macos/app/BridgingHeader.h import path.
5. Update AGENTS.md and any README references to the bridge location.
6. Verify CI passes on all platforms after the move.

Files

• frontend/macos/bridge/ — source location
• CMakeLists.txt (root)
• ewpresenter/tests/CMakeLists.txt
• frontend/macos/CMakeLists.txt
• frontend/macos/app/BridgingHeader.h
• AGENTS.md