- Convert milliseconds to datetime for GET filters (created_after/before, ended_after/before)
- Fix is_active filter to use is_null() instead of comparing to 0
- Fix PATCH to use datetime.now() instead of int timestamps
- Fix POST to convert timestamps and use None for nullable ended field
- Update Pydantic model defaults to None instead of int
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>