v1.0.2

Add auto-update via update.electronjs.org

Wire update-electron-app into the main process so packaged builds check
GitHub for newer published releases hourly and prompt to restart.

- New src/main/updater.ts (no-ops in dev / unsigned builds)
- Upload the macOS .zip and full Windows Squirrel output in CI so the
  Squirrel updaters have the files they need (not just the installers)
- Bump version to 1.0.2 so it stays in sync with the release tag