feat(tests): let managers escalate and directly resolve disputed tests

Request Discussion only ever nudged the peer lead, and the one-time
manager notification when a dispute starts had no real follow-up
action attached to it — a manager could be told a dispute existed but
had no way to actually do anything about it. Adds:

- POST /tests/{id}/escalate-to-manager — either lead can explicitly
  ask managers to step in, distinct from the passive initial notice.
- POST /tests/{id}/manager-resolve-dispute — a manager decides the
  final outcome (validated/rejected) directly, bypassing both leads'
  votes entirely, reusing the same dual-validation event dispatch so
  Jira/notifications behave like any other resolution.

Both leads are notified of the manager's final call, win or lose.

backend/app/services/test_workflow_service.py

@@ -1341,6 +1341,50 @@ def resolve_dispute(db: Session, test: Test, user: User, target_team: str, notes
     return test
 
 
+def resolve_dispute_by_manager(db: Session, test: Test, user: User, outcome: str, notes: str | None = None) -> Test:
+    """A manager makes the final call on a disputed test — validated or rejected.
+
+    Unlike ``resolve_dispute`` (only the approving lead flipping their own
+    vote), this is a manager override that ends the standoff directly,
+    without either lead having to concede. Reuses the same dual-validation
+    event dispatch as a normal in_review resolution so Jira/notifications
+    behave identically to an ordinary validated/rejected outcome.
+    """
+    if test.state != TestState.disputed:
+        raise InvalidOperationError("Test is not in disputed state")
+
+    entity = TestEntity.from_orm(test)
+    entity.resolve_dispute_by_manager(outcome)
+    entity.apply_to(test)
+    db.flush()
+
+    log_action(
+        db, user_id=user.id, action="manager_resolve_dispute",
+        entity_type="test", entity_id=test.id,
+        details={"outcome": outcome, "notes": notes, "test_name": test.name},
+    )
+
+    _dispatch_dual_validation_effects(db, test, entity, actor=user)
+
+    # Let both leads know the manager made the final call, not just whichever
+    # side "won" — the losing side needs to know just as much.
+    for lead_id in filter(None, {test.red_validated_by, test.blue_validated_by}):
+        try:
+            create_notification(
+                db, user_id=lead_id, type="manager_dispute_resolution",
+                title=f"Manager resolved disputed test as {outcome}",
+                message=(
+                    f'{user.username} resolved the dispute on "{test.name}" as {outcome}.'
+                    + (f" Notes: {notes}" if notes else "")
+                ),
+                entity_type="test", entity_id=test.id,
+            )
+        except Exception as e:
+            logger.warning("Notification failed for test %s: %s", test.id, e, exc_info=True)
+
+    return test
+
+
 # Define function handle_remediation_completed
 def handle_remediation_completed(db: Session, test: Test, user: User) -> Test | None:
     """Create a re-test when remediation is completed.