fix: event-specific custom CSS settings not being saved

The ThemeCustomizerEnhanced component stored customCss in a separate
local state that was never propagated to the parent component when
hideActions was true (used in both CreateEventPage and EventDetailsPage).

Changes:
- handleChange() now includes customCss when propagating theme changes
- CSS textarea onChange now propagates customCss to parent in preview mode
- handlePresetSelect() clears customCss when selecting a preset

Fixes #136

frontend/src/components/admin/ThemeCustomizerEnhanced.tsx

@@ -75,7 +75,8 @@ export const ThemeCustomizerEnhanced: React.FC<ThemeCustomizerEnhancedProps> = (
     }
 
     if (isPreviewMode) {
-      onChange(updated);
+      // Include customCss in the propagated theme
+      onChange({ ...updated, customCss });
     }
   };
 
@@ -84,6 +85,7 @@ export const ThemeCustomizerEnhanced: React.FC<ThemeCustomizerEnhancedProps> = (
     if (preset) {
       setSelectedPreset(presetKey);
       setLocalTheme(preset.config);
+      setCustomCss(''); // Clear custom CSS when selecting a preset
       if (onPresetChange) {
         onPresetChange(presetKey);
       }
@@ -722,12 +724,17 @@ export const ThemeCustomizerEnhanced: React.FC<ThemeCustomizerEnhancedProps> = (
         <textarea
           value={customCss}
           onChange={(e) => {
-            setCustomCss(e.target.value);
+            const newCss = e.target.value;
+            setCustomCss(newCss);
             // Mark as custom when CSS is added
-            if (e.target.value && selectedPreset !== 'custom' && onPresetChange) {
+            if (newCss && selectedPreset !== 'custom' && onPresetChange) {
               setSelectedPreset('custom');
               onPresetChange('custom');
             }
+            // Propagate customCss changes to parent in preview mode
+            if (isPreviewMode) {
+              onChange({ ...localTheme, customCss: newCss });
+            }
           }}
           placeholder="/* Add custom CSS here */"
           className="w-full h-40 px-3 py-2 font-mono text-sm border border-neutral-300 rounded-lg bg-neutral-50"