React 19 Test Migration Patterns

Reference for all test file migrations required by React 19.

Priority Order

Fix test files in this order; each layer depends on the previous:

1. act import fix first, it unblocks everything else
2. Simulate → fireEvent fix immediately after act
3. Full react-dom/test-utils cleanup remove remaining imports
4. StrictMode call counts measure actual, don't guess
5. Async act wrapping for remaining "not wrapped in act" warnings
6. Custom render helper verify once per codebase, not per test

1. act() Import Fix