fix(jira,tests): send real datetime to RT/BT date fields, resolve assignee usernames for operators

- RT/BT Start/End Date are genuine Jira "datetime" custom fields (confirmed
  via issue_editmeta), not plain dates. Pushing a bare "YYYY-MM-DD" string
  made Jira default the time-of-day to midnight, so RT Start Date and RT
  End Date ended up showing the same meaningless midnight timestamp instead
  of the actual execution window. Now sends a full ISO datetime.
- The test detail page showed "RT: Unassigned" for the operator who WAS
  correctly assigned, because GET /users/operators (the only source
  AssigneeControl used to resolve an assignee ID into a username) is
  restricted to leads/managers — a plain operator has no other way to
  resolve their own ID. TestOut now resolves and includes the assignee's
  username directly (red/blue tech + reviewer), so the badge no longer
  depends on a permission-gated list the viewer might not have access to.

backend/app/services/test_crud_service.py

@@ -396,6 +396,8 @@ def get_test_detail(db: Session, test_id: uuid.UUID) -> Test:
         .options(
             joinedload(Test.evidences), joinedload(Test.technique),
             joinedload(Test.round_history),
+            joinedload(Test.red_tech_assigned_user), joinedload(Test.blue_tech_assigned_user),
+            joinedload(Test.red_reviewer), joinedload(Test.blue_reviewer),
         )
         .filter(Test.id == test_id)
         # Chain .first() call