## What changed
- Add an optional opaque `providerId` to `externalAgentConfig/import` for analytics attribution, independently of the `migrationSource` selector.
- Include the provider ID in completed-import and import-failure analytics events.
- Have TUI imports identify their selected migration source as the provider.
## Testing
- Cover provider attribution in app-server import completion and failure tests and analytics serialization tests.
GitOrigin-RevId: 0ee7313a43652e5305939c526bf6b903a79334ad