Extract the engines and business layer into core/ (task 510c1f78)

Move presence.py, materialize.py, completion.py, events.py, children.py,
quest_definitions.py, admin_allowlist.py and service_policy.py into
custom_components/nestquest/core/, leaving re-export shims at the
original paths so the integration keeps working unchanged.

core/events.py is refactored to PAYLOAD CONSTRUCTION ONLY: it builds
and returns (event_type, payload) tuples and never touches hass.bus or
hass.config. The HA-local 'today' the day-complete rule needs is now a
parameter (read from hass.config.time_zone by the integration shim).
The events.py shim retains fire_quest_completed/fire_quest_uncompleted,
wiring the returned events to hass.bus.async_fire so the four event
names and payload shapes stay identical (nestquest_quest_completed with
was_on_time, nestquest_quest_uncompleted, nestquest_child_day_complete
with quests_due/quests_completed, occurred_at strict UTC ISO-8601).

Update two test logger-name references (children now logs as
...core.children) and the materialize _now_stamp monkeypatch target
(now patches the core module the walk reads globals from).

1497 passed (baseline). No homeassistant import under core/, no
top-level core import under the integration, no repo-root core/.

tests/test_materialize.py

@@ -1475,7 +1475,7 @@ async def _collect_records(database, child_ids, start, end) -> set:
 
 
 def test_materialize_end_to_end_six_rule_types(tmp_path, monkeypatch) -> None:
-    import custom_components.nestquest.materialize as materialize_module
+    import custom_components.nestquest.core.materialize as materialize_module
 
     # Give each materialize run a DISTINCT batch stamp: production upserts
     # rewrite generated_at on every re-run, so a shared pinned stamp would
@@ -1487,6 +1487,9 @@ def test_materialize_end_to_end_six_rule_types(tmp_path, monkeypatch) -> None:
         stamps["n"] += 1
         return f"2026-06-01T00:00:{stamps['n']:02d}+00:00"
 
+    # The materialize() walk reads ``_now_stamp`` from its OWN module
+    # globals (now the HA-free core package), so the patch must target
+    # the core module, not the re-export shim the integration imports.
     monkeypatch.setattr(materialize_module, "_now_stamp", _distinct_stamp)
 
     async def _body(database):