feat: new value source types (HA entity, gradient map, strip extract) + UI fixes

New value source types:
- ha_entity: reads numeric values from HA entity state/attribute, normalizes
  via min/max range, applies EMA smoothing. EntitySelect for HA connection
  and entity selection with live entity list fetching.
- gradient_map: maps a float value source (0-1) through a gradient entity.
  EntitySelect for both input source and gradient with inline previews.
- css_extract: extracts single color by averaging LED range from a color
  strip source. EntitySelect for source selection.

Value source type picker:
- Filter tabs (All / Numeric / Color) above the icon grid
- showTypePicker extended with filterTabs + onFilterChange support

Palette selectors converted to EntitySelect:
- Effect palette, gradient preset, and audio palette selectors now use
  command-palette style EntitySelect with gradient strip previews

Tab indicator fixes:
- Icon now updates on tab switch (was passing no args to updateTabIndicator)
- Visible with any background effect active, not just Noise Field
- Noise Field is the default background effect for new users

Dashboard section collapse fix:
- Split header into clickable toggle (chevron+label) and non-clickable
  actions area — buttons no longer trigger collapse/expand

Discriminated union fix (422 errors):
- source_type/target_type now always included in update payloads for:
  CSS editor, LED target, HA light target, simple calibration,
  advanced calibration

server/src/wled_controller/static/js/features/calibration.ts

@@ -241,9 +241,10 @@ export async function showCSSCalibration(cssId: any) {
         if (!source) { showToast(t('calibration.error.css_load_failed'), 'error'); return; }
         const calibration: Calibration = source.calibration || {} as Calibration;
 
-        // Set CSS mode — clear device-id, set css-id
+        // Set CSS mode — clear device-id, set css-id and source type
         (document.getElementById('calibration-device-id') as HTMLInputElement).value = '';
         (document.getElementById('calibration-css-id') as HTMLInputElement).value = cssId;
+        (document.getElementById('calibration-css-source-type') as HTMLInputElement).value = source.source_type || 'picture';
 
         // Populate device picker for edge test
         const testDeviceSelect = document.getElementById('calibration-test-device') as HTMLSelectElement;
@@ -931,9 +932,10 @@ export async function saveCalibration() {
     try {
         let response;
         if (cssMode) {
+            const cssSourceType = (document.getElementById('calibration-css-source-type') as HTMLInputElement).value || 'picture';
             response = await fetchWithAuth(`/color-strip-sources/${cssId}`, {
                 method: 'PUT',
-                body: JSON.stringify({ calibration, led_count: declaredLedCount }),
+                body: JSON.stringify({ source_type: cssSourceType, calibration, led_count: declaredLedCount }),
             });
         } else {
             response = await fetchWithAuth(`/devices/${deviceId}/calibration`, {