Vaadin UI backend

ui.web implements the backend-neutral ui protocols with Vaadin Flow. Widget composition, field observation, bindings, keyed reconciliation and resource ownership belong to ui; the web backend owns browser nodes, session scheduling and host integration.

The backend consumes ui.theme through the shared UI theme context. It does not depend on ui.desktop or ui.desktop.kit.

Implementation and acceptance entry points:

• Module and backend sources.
• Host integration and lifecycle.
• Runnable applications.
• Host tests.
• Build instructions and supported execution modes.

Java integration uses the existing adapter mechanism. Vaadin-specific types and scheduling remain in the backend repository; the compiler has no Vaadin-specific behavior.