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/static/css/modal.css

@@ -1738,6 +1738,31 @@
     background: var(--border-color);
 }
 
+/* ── Weather source location row ── */
+
+.weather-location-row {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    flex-wrap: wrap;
+}
+
+.weather-location-field {
+    display: flex;
+    align-items: center;
+    gap: 4px;
+}
+
+.weather-location-field label {
+    font-size: 0.85rem;
+    color: var(--text-secondary);
+    flex-shrink: 0;
+}
+
+.weather-location-field input[type="number"] {
+    width: 80px;
+}
+
 .composite-layer-drag-handle:active {
     cursor: grabbing;
 }