Add app migration to ToDesktop.
An existing Electron app can now move its installed user base over to a
ToDesktop app by shipping one final update through its current update channel.
Declare the migration with
todesktop.init({ migration: { targetAppId: "your-todesktop-app-id" } }) (or a
todesktop-migration.json file in the app's resources); the installed app then
updates in place into the ToDesktop build and updates normally from then on.
Supported on Windows, macOS (same signing team), and Linux (AppImage), with any
build tooling — including Electron Forge. Apps originally installed with
Squirrel.Windows can have the legacy installation cleaned up automatically via
windows.migrationSource.squirrelPackageName in todesktop.json. See the
@todesktop/runtime README for the full migration guide.