feat: harden PR queue reconciliation against stale/conflicting state (#166)

- Add updated_at (list_prs), + merged_at/merge_commit_sha/closed_at/updated_at (view_pr) for staleness detection in tool output and inventory.
- Surface updated_at in gitea_review_pr inventory report.
- Strengthen gitea-pr-review skill steps, _COMMON_WORKFLOWS, _GUIDE_RULES with explicit live reconciliation checklist, 'do not trust prior handoffs', stop on conflict.
- Add dedicated live queue reconciliation runbook section in docs/llm-workflow-runbooks.md.
- Add passthrough tests and assertions for new fields.
- All gates, redaction, author/reviewer separation untouched.
- Tests pass, py_compile clean, diff clean, secret sweep clean.

Closes #166

tests/test_pr_queue_inventory.py

@@ -56,7 +56,8 @@ class TestPRQueueInventory(unittest.TestCase):
                 "mergeable": True,
                 "user": {"login": "jcwalker3"},
                 "labels": [{"name": "bug"}],
-                "body": "Fixes #10"
+                "body": "Fixes #10",
+                "updated_at": "2026-07-05T10:00:00Z"
             },
             {
                 "number": 2,
@@ -67,7 +68,8 @@ class TestPRQueueInventory(unittest.TestCase):
                 "mergeable": True,
                 "user": {"login": "other_user"},
                 "labels": [],
-                "body": ""
+                "body": "",
+                "updated_at": "2026-07-05T11:00:00Z"
             }
         ]
         mock_api.return_value = {"login": "jcwalker3"} # whoami
@@ -80,6 +82,8 @@ class TestPRQueueInventory(unittest.TestCase):
         self.assertIn("Review/merge blocked (Self-author). Requires a genuine non-author reviewer", result["message"])
         self.assertIn("Review/merge blocked (Current profile is Author)", result["message"])
         self.assertIn("gitea_activate_profile", result["message"])
+        # updated_at surfaced for reconciliation (#166)
+        self.assertIn("Updated: 2026-07-05T10:00:00Z", result["message"])
 
     @patch("mcp_server.api_get_all")
     @patch("mcp_server.api_request")