Most of the web suite's console noise came from tests opting into React's act
environment for the whole test while driving the UI with real browser events,
plus components rendered without a router. Add a shared render helper built on
vitest-browser-react that only enables the act environment inside act(), wraps
the tree in a memory router, and re-renders in place per container. Migrate the
nine noisiest browser test files to it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>