Electron CI on GitHub Actions

Every platform build downloads Electron binaries and rebuilds native modules.

Why it happens

The Electron download cache and node-gyp build outputs are not persisted across runs.

What to change

1. Cache ~/.cache/electron and ~/.cache/electron-builder
2. Build macOS, Windows and Linux targets as parallel matrix legs on native runners
3. Cache the node-gyp build directory so native modules are not recompiled

Electron on runnerhut

jobs:
  build:
    strategy:
      matrix:
        include:
          - os: runnerhut-8vcpu-ubuntu-2404
          - os: runnerhut-macos-15-m4
          - os: runnerhut-8vcpu-windows-2022
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v4
      - run: npm ci && npx electron-builder --publish never

The only runnerhut-specific line is `runs-on: runnerhut-8vcpu-ubuntu-2404`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.