feat: add weather source entity and weather-reactive CSS source type

New standalone WeatherSource entity with pluggable provider architecture
(Open-Meteo v1, free, no API key). Full CRUD, test endpoint, browser
geolocation, IconSelect provider picker, CardSection with test/clone/edit.

WeatherColorStripStream maps WMO weather codes to ambient color palettes
with temperature hue shifting and thunderstorm flash effects. Ref-counted
WeatherManager polls API and caches data per source.

CSS editor integration: weather type with EntitySelect source picker,
speed and temperature influence sliders. Backup/restore support.

i18n for en/ru/zh.

server/src/wled_controller/api/routes/backup.py

@@ -55,6 +55,7 @@ STORE_MAP = {
     "automations": "automations_file",
     "scene_presets": "scene_presets_file",
     "gradients": "gradients_file",
+    "weather_sources": "weather_sources_file",
 }
 
 _SERVER_DIR = Path(__file__).resolve().parents[4]