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/people_flow_project/tests/test_webhook.py

@@ -5,7 +5,7 @@ import json
 from src.people_flow.webhook import dispatch_json_event
 
 
-def test_dispatch_json_event_omits_tracks_from_webhook_but_keeps_local_log(
+def test_dispatch_json_event_does_not_post_half_hour_report_but_keeps_local_log(
     tmp_path, monkeypatch
 ):
     sent: dict[str, object] = {}
@@ -44,9 +44,4 @@ def test_dispatch_json_event_omits_tracks_from_webhook_but_keeps_local_log(
 
     lines = output.read_text(encoding="utf-8").splitlines()
     assert json.loads(lines[0]) == payload
-    assert sent["url"] == "https://example.test/webhook"
-    assert sent["timeout"] == 7.5
-    assert sent["payload"] == {
-        "event": "half_hour_report",
-        "total_people": 3,
-    }
+    assert sent == {}