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>

plugin-repos/starlark-apps/manager.py

@@ -18,6 +18,7 @@ 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
 
@@ -228,6 +229,10 @@ 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")
@@ -816,6 +821,10 @@ 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),