Add filtering to task list:
- GET /tasks accepts query params: ?status=open&priority=1&namespace=Omni/Jr
- Add filter form above task table with dropdowns
- Status dropdown: All, Open, InProgress, Review, Approved, Done
- Priority dropdown: All, P0-P4
- Namespace text input (optional)
- Form submits via GET to preserve filters in URL
- Filters are AND combined