fix(jira): clear stale assignee on hand-off to blue team / dual validation

The red_lead reviewer stayed assigned in Jira through blue_evaluating
(and the blue_lead reviewer through in_review) since push_test_event
never touched the assignee on those transitions — only red_executing
and the review gates did. Both are hand-offs with no single owner yet,
so the assignee is cleared instead of left stale.

Also fixes push_bt_work_started never assigning the blue_tech who
actually picks up the queued test — it only moved the status to
In Progress before.

backend/app/services/jira_service.py

@@ -859,6 +859,21 @@ def push_test_event(
                         link.jira_issue_key, jira_account_id, exc_a,
                     )
 
+        # Both are hand-off points to a different team with no single owner
+        # yet: blue_evaluating is queued for Blue Team (whoever reviewed the
+        # red side is done with it), and in_review is dual-validation by both
+        # leads at once. Leaving the previous assignee (red/blue reviewer)
+        # stuck on the ticket is misleading, so clear it.
+        if new_state in ("blue_evaluating", "in_review"):
+            try:
+                jira.assign_issue(link.jira_issue_key, account_id=None)
+                logger.info("Unassigned Jira ticket %s (state=%s)", link.jira_issue_key, new_state)
+            except Exception as exc_a:
+                logger.warning(
+                    "Could not unassign %s for state %s: %s",
+                    link.jira_issue_key, new_state, exc_a,
+                )
+
         link.last_synced_at = datetime.utcnow()
         db.flush()
         logger.info(
@@ -1067,6 +1082,16 @@ def push_bt_work_started(db: Session, test, actor) -> None:
         except Exception as exc_t:
             logger.warning("Could not transition %s to In Progress: %s", link.jira_issue_key, exc_t)
         jira.issue_add_comment(link.jira_issue_key, comment)
+
+        jira_account_id = getattr(actor, "jira_account_id", None)
+        if jira_account_id:
+            try:
+                jira.assign_issue(link.jira_issue_key, account_id=jira_account_id)
+            except Exception as exc_a:
+                logger.warning(
+                    "Could not assign %s to %s: %s", link.jira_issue_key, jira_account_id, exc_a,
+                )
+
         link.last_synced_at = datetime.utcnow()
         db.flush()
         logger.info("Posted blue-team-started event to Jira %s", link.jira_issue_key)