Add effect palette preview bar in CSS editor

Show a gradient color bar below the effect type description, giving
users a visual preview of palette colors before applying. Updates
live when switching effect type, palette, or meteor head color.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/js/app.js

@@ -89,7 +89,8 @@ import {
 // Layer 5: color-strip sources
 import {
     showCSSEditor, closeCSSEditorModal, forceCSSEditorClose, saveCSSEditor, deleteColorStrip,
-    onCSSTypeChange, onEffectTypeChange, onAnimationTypeChange, colorCycleAddColor, colorCycleRemoveColor,
+    onCSSTypeChange, onEffectTypeChange, onAnimationTypeChange, updateEffectPreview,
+    colorCycleAddColor, colorCycleRemoveColor,
     applyGradientPreset,
 } from './features/color-strips.js';
 
@@ -277,6 +278,7 @@ Object.assign(window, {
     onCSSTypeChange,
     onEffectTypeChange,
     onAnimationTypeChange,
+    updateEffectPreview,
     colorCycleAddColor,
     colorCycleRemoveColor,
     applyGradientPreset,