Coordinator polls the API snapshot and rebuilds the sensors' data

Feature 18: the shared coordinator's refresh pass now fetches
GET /api/v1/panel/snapshot through the NestQuestApiClient and
reconstructs the exact core dataclasses (NestQuestSnapshot,
ChildDaySnapshot, QuestInstanceView) the Feature 10 entities read, so
sensor.py and binary_sensor.py are untouched and every entity_id and
attribute payload keeps its shape.

Why: the integration becomes an API client of the NestQuest service
instead of a second reader of the SQLite file, and the panel cards and
the four blueprints keep working without changes.

- snapshot_from_api_payload maps the route's JSON back onto the
  dataclasses field by field (state 'completed' -> 'done' so
  instance_payload renders 'completed' again; counts, presence,
  next_present, overdue, on_time, completed_at pass through verbatim;
  due_date is stamped from today_iso, the only date the route serves).
- The panel payload omits missed instances (D-009), so
  admin_instances can no longer carry missed rows — the admin surface
  for missed quests is the PWA reading the API directly. Documented in
  the module docstring and pinned by tests.
- An unconfigured panel token (the shipped default) gets a typed-error
  stub instead of a construction crash: setup succeeds, the first
  refresh fails cleanly, entities come up unavailable and HA's retry
  cycle applies. Fetch failures log the typed error and mark the
  entities unavailable while data keeps its last good snapshot.
- The runtime record registers before the first refresh so the refresh
  path always finds the live entry state; the update interval and the
  serialized forced-refresh behaviour are unchanged.
- Tests: a fixture snapshot drives the coordinator (stub client, no
  network) asserting per-child values, household rollups, cycle day,
  and the exact instance payload shape, plus unconfigured and
  failed-fetch cases; DB-seeded tests ride a lazy local-snapshot
  client through the same JSON path.

tests/test_entity_matrix.py

@@ -180,9 +180,12 @@ async def test_entity_and_event_matrix(hass, make_entry) -> None:
     assert _sensor(hass, ada.id, "all_done").is_on is False
     assert _sensor(hass, ada.id, "quests_remaining_today").native_value == 1
 
-    # --- The instances payload omits missed instances while
-    # admin_instances includes them (D-009): pin the derive clock
-    # forward in the TEST ONLY so today's open instances read missed.
+    # --- The instances payload omits missed instances (D-009) — and
+    # since Feature 18 the snapshot comes from the API panel route,
+    # which omits missed rows ENTIRELY, so admin_instances cannot
+    # carry them either (the admin surface for missed quests is the
+    # PWA, reading the API directly): pin the derive clock forward in
+    # the TEST ONLY so today's open instances read missed.
     original_refresh = coordinator._async_update_data
 
     async def _future_dated_refresh():
@@ -203,9 +206,9 @@ async def test_entity_and_event_matrix(hass, make_entry) -> None:
     await coordinator.async_refresh()
     attributes = _sensor(hass, bo.id, "quests_due_today").extra_state_attributes
     assert attributes["instances"] == [], "panel payload omits missed"
-    assert len(attributes["admin_instances"]) == 2
-    assert all(
-        entry["state"] == "missed" for entry in attributes["admin_instances"]
+    assert attributes["admin_instances"] == [], (
+        "the API payload omits missed rows, so the admin payload "
+        "carries none either (the PWA is the admin surface now)"
     )
     coordinator._async_update_data = original_refresh
     await coordinator.async_refresh()