[Aug 4, 2026] Case Closed Date on Docket Records

Docket records now include a date_closed field: the date a case was closed or terminated, when known. It is null when the case is still open or the date is unavailable. The field appears on docket responses returned by the docket search and docket detail endpoints (for example GET /docket_searches/{search_request_id} and GET /dockets/{docket_id}/details), alongside the existing date_filed.

Case status derivation is also more accurate: open, opened, reopen, and reopened states are all treated as open, and Chapter 15 and other active/inactive edge cases are classified correctly.

No integration changes required. the field is additive and nullable.