Add todo_md_staleness State Hub context resolver

Supports daily TODO.md stale-review ActivityDefinition via
GET /repos/todo-md-staleness.

tests/test_state_hub_context_resolver.py

@@ -192,6 +192,55 @@ def test_repo_sbom_status_bulk_returns_worst_repo(monkeypatch) -> None:
     assert by_slug["never-scanned"]["last_sbom_at"] is None
 
 
+def test_todo_md_staleness_returns_stale_repos(monkeypatch) -> None:
+    calls: list[dict[str, Any]] = []
+
+    def fake_get(url: str, **kwargs: Any) -> DummyResponse:
+        calls.append({"url": url, **kwargs})
+        return DummyResponse({
+            "stale_days": 6,
+            "repos": [
+                {
+                    "repo_slug": "markitect-main",
+                    "has_todo": True,
+                    "age_days": 12,
+                    "mtime": "2026-06-26T10:00:00+00:00",
+                    "todo_path": "/home/worsch/markitect-main/TODO.md",
+                }
+            ],
+            "stale_count": 1,
+            "total_with_todo": 1,
+            "total_scanned": 62,
+            "worst_repo_slug": "markitect-main",
+            "worst_age_days": 12,
+        })
+
+    monkeypatch.setenv("STATE_HUB_URL", "http://state-hub.test")
+    monkeypatch.setattr(httpx, "get", fake_get)
+
+    result = StateHubContextResolver().resolve(
+        "todo_md_staleness", None, {"stale_days": 6}
+    )
+
+    assert calls == [{
+        "url": "http://state-hub.test/repos/todo-md-staleness",
+        "params": {"stale_days": 6},
+        "timeout": 10.0,
+    }]
+    assert result["stale_count"] == 1
+    assert result["repos"][0]["repo_slug"] == "markitect-main"
+
+
+def test_todo_md_staleness_returns_empty_on_failure(monkeypatch) -> None:
+    def fake_get(url: str, **kwargs: Any) -> DummyResponse:
+        return DummyResponse(None, status_error=httpx.HTTPError("boom"))
+
+    monkeypatch.setenv("STATE_HUB_URL", "http://state-hub.test")
+    monkeypatch.setattr(httpx, "get", fake_get)
+
+    assert StateHubContextResolver().resolve("todo_md_staleness", None, {}) == {}
+
+
 def test_repo_sbom_status_returns_empty_on_failure(monkeypatch) -> None:
     def fake_get(url: str, **kwargs: Any) -> DummyResponse:
         return DummyResponse(None, status_error=httpx.HTTPError("boom"))