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/tests/test_test_entity.py

@@ -246,6 +246,15 @@ def test_reopen_red_review_moves_to_red_executing():
     assert any(ev.name == "red_review_reopened" for ev in e.events)
 
 
+def test_reopen_red_review_starts_timer_paused():
+    """The timer must not run until the operator explicitly resumes it —
+    otherwise Tempo worklogs and operation-time metrics count time the
+    lead spent reviewing, not time the operator spent working."""
+    e = _entity("red_review")
+    e.reopen_red_review()
+    assert e.paused_at == e.red_started_at
+
+
 def test_reopen_red_review_wrong_state():
     e = _entity("blue_evaluating")
     with pytest.raises(InvalidStateTransition):