Move diff parsing to worker pool with stable patch cache keys

- Wrap `DiffPanel` in `WorkerPoolContextProvider` and add a dedicated diffs worker
- Use content-based patch cache keys to stabilize `parsePatchFiles` caching
- Add tests for cache key stability, whitespace normalization, and content changes
ba46a1b9a6Julius Marminge committed on 2/18/2026, 11:58:54 PMparenta2e4c71
4 files changedLine totals unavailable