v0.1.12

feat: remove --onefile, use directory mode for faster builds

PyInstaller: --onefile → --onedir (default)
Nuitka: --onefile removed, --standalone only

Benefits:
- Faster build time (no compression/packing overhead)
- Faster app startup (no temp extraction on Windows)
- All dependencies still bundled in backend_bin/<flavor>/ directory

Also includes:
- Real-time startup log viewer in BackendGate
- Simplified CI: no binary rename step, cleaner Release upload
- main.js: resolveBackendBinary() searches subdirectories with
  legacy flat-file fallback