Adopt Home Assistant's time zone for the API household clock

The deployed API host runs UTC and the household `timezone` setting was
never set, so the panel snapshot read UTC: morning quests showed overdue
hours early and `today_iso` rolled over at UTC midnight.

The integration now reports `hass.config.time_zone` on every panel
request (`X-NestQuest-Timezone`).  While the admin has not chosen a zone
(`timezone_configured` is false) the API adopts and persists it, so the
panel, the admin plane, and the missed-sweep scheduler all read the
household clock out of the box.  An explicit admin choice — including an
explicitly chosen empty zone — still wins; an invalid reported zone is
logged and ignored.  No schema change.

Task: 6351b36d-0eef-4e7d-bf5a-96b754cbc883

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

custom_components/nestquest/core/settings.py

@@ -327,12 +327,14 @@ class NestQuestSettings:
     def household_now(self, instant: datetime.datetime) -> datetime.datetime:
         """Return the aware ``instant`` expressed in the household's zone.
 
-        The API service has no Home Assistant ``time_zone``, so its one
+        The API service does not run inside Home Assistant, so its one
         clock read (an aware host-local ``now``) is converted here: with
-        :attr:`timezone` set the SAME instant is re-expressed in that
-        zone, so ``.date()`` and ``.time()`` are the household's wall
-        clock even when the host runs UTC.  With :attr:`timezone` empty
-        the instant is returned unchanged (the host's local time).
+        :attr:`timezone` set — the admin's choice, or else the zone the
+        integration reports from Home Assistant — the SAME instant is
+        re-expressed in that zone, so ``.date()`` and ``.time()`` are the
+        household's wall clock even when the host runs UTC.  With
+        :attr:`timezone` empty the instant is returned unchanged (the
+        host's local time).
         """
         if not self.timezone:
             return instant