Async event handlers (via Watermill) from the previous test can hold
SQLite connections, starving the next test's fixture setup PATCH request.
Three changes fix this:
1. Track in-flight event handler goroutines with a WaitGroup.
2. Call WaitForPendingHandlers() in the test endpoint before
truncating/inserting data.
3. Navigate the browser to about:blank in fixture teardown to stop
notification polling and other frontend requests between tests.
kolaente