feat(I3): always-on pipeline status indicator in the top nav

New /api/system/activity/summary aggregates scheduler health + per-queue
pending depths + running count + 24h failure count in one cached call (safe
to poll app-wide). PipelineStatusChip lives in the TopNav on every page: a
compact running/queued/failing chip with a scheduler-health dot that expands
to a popover (scheduler, busy queues, counts, link to downloads). Polls the
summary every 8s, paused when backgrounded. Reuses the queue-cache read via
_queues_cached(). + API test for the summary shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_api_system_activity.py

@@ -44,6 +44,25 @@ async def test_queues_returns_all_known_queues(client, monkeypatch):
     assert set(body["queues"].keys()) == set(activity_module._QUEUE_NAMES)
 
 
+@pytest.mark.asyncio
+async def test_summary_returns_rollup_shape(client, monkeypatch):
+    def _fake():
+        return {
+            "queues": {**dict.fromkeys(activity_module._QUEUE_NAMES, 0), "ml": 3},
+            "fetched_at": datetime.now(UTC).isoformat(),
+        }
+    monkeypatch.setattr(activity_module, "_read_queues_sync", _fake)
+
+    resp = await client.get("/api/system/activity/summary")
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert set(body.keys()) == {"scheduler", "queues", "queued_total", "running", "failing"}
+    assert body["queued_total"] == 3  # only ml has a non-zero depth
+    assert isinstance(body["running"], int)
+    assert isinstance(body["failing"], int)
+    assert set(body["scheduler"]) == {"last_tick_at", "next_due_at", "due_now", "auto_sources"}
+
+
 @pytest.mark.asyncio
 async def test_queues_cached_within_ttl(client, monkeypatch):
     call_count = {"n": 0}