feat(review): review queue for leads + manual reviewer reassignment

Leads get the same two-queue view operators already have: 'Available
to Review' (pending reviews currently assigned to a peer lead) and
'My Assigned Reviews' (assigned to me), replacing the old single
'My Reviews' toggle. Since the load-balanced auto-assignment always
picks a reviewer immediately, 'available' means peer-assigned reviews
a lead could pick up if the assignee can't get to them, not unclaimed
ones (there aren't any).

POST /tests/{id}/assign now also accepts red_reviewer_assignee /
blue_reviewer_assignee, validated against the matching lead role and
synced to Jira the same way operator assignment already is. The
AssigneeControl UI gained a 'reviewer' kind (leads-only picker) shown
on the test detail header while a test sits in red_review/blue_review
— this also fixes the reviewer assignment being invisible in Aegis
even though it was already being pushed to Jira correctly.

backend/app/schemas/test.py

@@ -171,10 +171,12 @@ class TestRemediationUpdate(BaseModel):
 
 
 class TestAssign(BaseModel):
-    """Payload for assigning operators to a test."""
+    """Payload for assigning operators or reviewers to a test."""
 
     red_tech_assignee: uuid.UUID | None = None
     blue_tech_assignee: uuid.UUID | None = None
+    red_reviewer_assignee: uuid.UUID | None = None
+    blue_reviewer_assignee: uuid.UUID | None = None
 
 
 class TestHold(BaseModel):