Add API, type and wire-protocol safety nets for the Angular package #37

Part of the core extraction (#35). Add safety nets around ngx-ui-watchtower as it is today, before any code moves, so the later parts can prove they change nothing for consumers.

Scope

• A public API snapshot with npm run api:check, run in CI.
• Type tests: the typed-names registry, augmented and empty, and the compatibility of the public types.
• A broadcast wire test with a recorded fixture, comparing a shell and a fragment's exchange, independent of machine paths and times.

Done when

• No production source changes.
• All checks pass on main's source.