v0.1.1

ci: drop Intel macOS build, ship three platforms (#20)

GitHub free Intel (macos-13) runners are chronically queued and macos-13 is
being deprecated, so every release was held hostage waiting for one. Apple
Silicon covers every Mac since late 2020, so we drop the Intel target and ship
Windows + macOS (Apple Silicon) + Linux. Intel-Mac users build from source.

- release.yml: remove the macos-13 matrix entry.
- electron-builder.yml: note mac is arm64-only.
- README / RELEASING / web guide: drop the Intel download, point Intel users to
  build-from-source.