docs(starlark): say what happens when the device location can't be used

A blank app Location only renders at the device's city when one is set and
the Open-Meteo lookup finds it. With no city, no match, or the geocoder
unreachable (retried after 30 minutes), the app gets no location and keeps
its author's default. The guide, the config page hint, CONFIG_REFERENCE and
the CHANGELOG entry now say so.

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

web_interface/templates/v3/partials/starlark_config.html

@@ -221,7 +221,7 @@
                                    data-starlark-location-key="timezone">
                         </div>
                     </div>
-                    <p class="text-xs text-gray-500 mt-1">Leave latitude and longitude blank to use this device's location (City / State / Country in General settings).</p>
+                    <p class="text-xs text-gray-500 mt-1">Leave latitude and longitude blank to use this device's location (City / State / Country in General settings). If no city is set there, or it can't be looked up, the app uses its own default.</p>
                     {% if field_desc %}
                     <p class="text-xs text-gray-400 mt-1">{{ field_desc }}</p>
                     {% endif %}