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/domain/test_entity.py

@@ -414,10 +414,14 @@ class TestEntity:
         Called when the assigned Red Lead sends the work back for rework.
         Resets the red-phase timer for a fresh attempt (the first attempt's
         worklog was already recorded at submit time, so this loses nothing).
+        Starts the timer PAUSED — the operator hasn't resumed working yet,
+        just because the lead reopened it. It only starts counting once they
+        explicitly resume it, same as coming back from a hold.
         """
         self._transition(TestState.red_executing)
         self.red_started_at = datetime.utcnow()
         self.red_paused_seconds = 0
+        self.paused_at = self.red_started_at
         self._events.append(DomainEvent("red_review_reopened"))
 
     # Define function submit_blue_evidence