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>

docs/STARLARK_APPS_GUIDE.md

@@ -139,9 +139,10 @@ Each app may have different configuration options:
 
 - **Location** (lat/lng/timezone): For weather, clocks, transit. Left blank,
   the app renders at this device's location (City / State / Country under
-  General settings). Without that, most community apps fall back to their
-  author's hard-coded default, usually San Francisco. Fill it in only to
-  point one app somewhere else.
+  General settings). If no city is set there, or the city can't be looked up
+  (no match, or the geocoder is unreachable -- retried after 30 minutes), the
+  app gets no location and falls back to its author's hard-coded default,
+  usually San Francisco. Fill it in only to point one app somewhere else.
 - **API Keys**: For services like weather, stocks, sports scores
 - **Display Preferences**: Colors, units, layouts
 - **Dropdown Options**: Team selections, language, themes