fix(tests): pause reopen timer, lock edits to assignee, restore Jira operator on reopen

- reopen_red_review starts the timer paused (paused_at set) instead of
  immediately running, since the operator hasn't resumed working yet —
  blue already did this via blue_work_started_at, red needed the same
  behavior via the existing pause/resume mechanism.
- update_test_red/update_test_blue now lock edits to the actual assigned
  operator for leads too, not just techs — a lead could previously edit
  another operator's in-progress test. Mirrored in TeamTabs.tsx.
- push_test_event reassigns the Jira ticket to the original operator
  (not the reopening lead) when a test returns to red_executing or
  blue_evaluating for rework, instead of leaving it on the lead.

backend/app/services/test_workflow_service.py

@@ -410,7 +410,14 @@ def reopen_red_review(db: Session, test: Test, user: User, notes: str) -> Test:
 
     try:
         from app.services.jira_service import push_test_event
-        push_test_event(db, test, user, "red_executing", extra={"notes": notes.strip()})
+        original_operator = (
+            db.query(User).filter(User.id == test.red_tech_assignee).first()
+            if test.red_tech_assignee else None
+        )
+        push_test_event(
+            db, test, user, "red_executing",
+            extra={"notes": notes.strip()}, assignee=original_operator,
+        )
     except Exception as e:
         logger.warning("Jira push failed for test %s: %s", test.id, e, exc_info=True)