fix(starlark): blank app locations use the device location, not San Francisco (#617)

* fix(starlark): blank app locations use the device location, not San Francisco

A Starlark (Tidbyt) app whose Location field is blank rendered at its
author's hard-coded DEFAULT_LOCATION -- usually San Francisco -- even with
the device city set under General settings. A user in Charlotte, NC got San
Francisco weather and radar with nothing in config.json to explain it.

src/device_location.py fills unset location fields at render time (display
plugin and the web standalone render): the device city is geocoded once via
Open-Meteo, preferring a match in the configured state/country, and cached
permanently. A saved location always wins; if the lookup fails the field is
dropped so the app uses its own default, and the failure is not retried for
30 minutes.

Also fixes the config form: clearing a location omitted the key, and the
save merges, so the old value could never be removed.

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

* 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>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

plugin-repos/starlark-apps/manager.py

@@ -19,6 +19,7 @@ from PIL import Image
 
 from src.plugin_system.base_plugin import BasePlugin, VegasDisplayMode
 from src.logging_config import get_logger
+from src.device_location import DeviceLocationResolver, apply_device_location
 from pixlet_renderer import PixletRenderer
 from frame_extractor import FrameExtractor
 
@@ -229,6 +230,10 @@ class StarlarkAppsPlugin(BasePlugin):
         self.current_app: Optional[StarlarkApp] = None
         self.last_update_check = 0
 
+        # Unset location fields render at the device's location, not the
+        # app author's default (usually San Francisco).
+        self.device_location = DeviceLocationResolver(cache_manager, self.logger)
+
         # Check Pixlet availability
         if not self.pixlet.is_available():
             self.logger.error("Pixlet not available - Starlark apps will not work")
@@ -882,6 +887,10 @@ class StarlarkAppsPlugin(BasePlugin):
             # Filter out LEDMatrix-internal timing/sizing keys before passing to pixlet
             INTERNAL_KEYS = {'render_interval', 'display_duration', 'render_width', 'render_height'}
             pixlet_config = {k: v for k, v in app.config.items() if k not in INTERNAL_KEYS}
+            # Applied here rather than saved into config.json, so a later
+            # change to the device location reaches the next render.
+            pixlet_config = apply_device_location(
+                pixlet_config, app.schema, self.device_location, self.global_config)
 
             success, error = self.pixlet.render(
                 star_file=str(app.star_file),