feat: improve webhook filtering, worker status startup handling, and timestamp parsing

- Skip half_hour_report events from webhook posts in people_flow
- Handle pre-existing stale worker status files during startup gracefully
- Make store_dwell_alert timestamp parsing robust against invalid/empty values
- Update lessons learned and todo documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

managed/store_dwell_alert/tests/test_manage_api.py

@@ -52,7 +52,7 @@ def build_client(project_root: Path):
                             "over_threshold_count": 2,
                             "under_threshold_count": 1,
                             "queue_level": "normal",
-                            "previous_queue_level": null,
+                            "previous_queue_level": None,
                             "status_change": "initial",
                         },
                     }
@@ -149,6 +149,39 @@ def test_get_manage_summary(tmp_path: Path):
     )
 
 
+def test_get_manage_summary_ignores_invalid_report_timestamp(tmp_path: Path):
+    client, _ = build_client(tmp_path)
+    events_path = tmp_path / "logs" / "events.jsonl"
+    with events_path.open("a", encoding="utf-8") as handle:
+        handle.write(
+            json.dumps(
+                {
+                    "event": "half_hour_report",
+                    "camera_id": "store_cam_01",
+                    "window_start": "2026-04-16T10:00:00+08:00",
+                    "window_end": "",
+                    "active_customer_count": 1,
+                    "queue_metrics": {
+                        "queue_level": "normal",
+                        "over_threshold_count": 1,
+                        "under_threshold_count": 0,
+                        "status_change": "unchanged",
+                    },
+                }
+            )
+            + "\n"
+        )
+
+    response = client.get("/api/manage/summary")
+
+    assert response.status_code == 200
+    assert response.json["last_result_time"] == "2026-04-16T10:00:00+08:00"
+    assert (
+        response.json["metrics"]["recent_window_stats"][0]["window_end"]
+        == "2026-04-16T10:00:00+08:00"
+    )
+
+
 def test_get_manage_windows(tmp_path: Path):
     client, _ = build_client(tmp_path)