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/templates/index.html

@@ -210,6 +210,7 @@
     {% include 'modals/value-source-editor.html' %}
     {% include 'modals/test-value-source.html' %}
     {% include 'modals/sync-clock-editor.html' %}
+    {% include 'modals/weather-source-editor.html' %}
     {% include 'modals/settings.html' %}
 
     {% include 'partials/tutorial-overlay.html' %}