Remove every automatic timezone-setting mechanism (task 7f685179)

The application timezone is now only ever set by an admin saving it:

- API: drop adopt_reported_timezone; the panel household clock reads the
  stored settings only and ignores any timezone request header.
- Integration: stop reporting Home Assistant's time_zone in an
  X-NestQuest-Timezone header (snapshot, completion and SSE requests).
- Admin app: remove the browser-zone detection and the automatic PATCH
  on load; the timezone field stays a manual control.
- Remove the timezone_configured marker from the core settings, the
  settings store and the admin settings API. A stored document that
  still carries the key loads harmlessly (unknown keys are ignored).

Tests replace the adoption expectations with proofs that a panel
timezone header never changes the stored settings, a fresh install's
empty zone stays empty with no settings write, the admin settings carry
no timezone_configured, and a manual admin timezone PATCH persists.

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

custom_components/nestquest/coordinator.py

@@ -372,10 +372,7 @@ def coordinator_client_from_entry(
         return _UnconfiguredApiClient()
     if session_factory is not None:
         return NestQuestApiClient(
-            base_url,
-            panel_token,
-            session_factory(hass),
-            household_timezone=hass.config.time_zone,
+            base_url, panel_token, session_factory(hass)
         )
     from custom_components.nestquest.api_client import client_from_entry