feat: add PR-only queue cleanup mode with per-PR dispatch gates (Closes #390)

Adds canonical pr-queue-cleanup workflow, report verifier, reviewer-only task
routing, and runbook guidance so operators can drain open PRs one canonical
review at a time with fail-closed boundaries on batching and unauthorized merges.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_role_session_router.py

@@ -99,6 +99,24 @@ class TestRoleSessionRouter(unittest.TestCase):
         self.assertFalse(route["downstream_allowed"])
         self.assertIn("Wrong role/session for reviewer task", route["message"])
 
+    def test_pr_queue_cleanup_under_author_profile_wrong_role_stop(self):
+        with patch.dict(os.environ, self._env("prgs-author")):
+            route = mcp_server.gitea_route_task_session(
+                task_type="pr_queue_cleanup", remote="prgs"
+            )
+        self.assertEqual(route["route_result"], role_session_router.ROUTE_WRONG_ROLE)
+        self.assertFalse(route["downstream_allowed"])
+
+    @patch("mcp_server.api_request", return_value={"login": "sysadmin"})
+    @patch("mcp_server.get_auth_header", return_value="token reviewer-pass")
+    def test_pr_queue_cleanup_under_reviewer_profile_allowed(self, _auth, _api):
+        with patch.dict(os.environ, self._env("prgs-reviewer")):
+            route = mcp_server.gitea_route_task_session(
+                task_type="pr_queue_cleanup", remote="prgs"
+            )
+        self.assertEqual(route["route_result"], role_session_router.ROUTE_ALLOWED)
+        self.assertTrue(route["downstream_allowed"])
+
     @patch("mcp_server.api_request")
     @patch("mcp_server.get_auth_header", return_value="token author-pass")
     def test_issue_creation_blocked_after_reviewer_wrong_role_stop(