Refactor asset image handling in event theme form.

Ensure asset_image_urls are merged instead of replaced during updates. Add a useEffect hook to log theme assets when editing an existing theme. These changes improve data handling consistency and debugging clarity.

frontend/src/components/event-themes/event-theme-form.tsx

@@ -57,7 +57,9 @@ export function EventThemeForm({ theme, mode }: ThemeFormProps) {
       background: "#FFFFFF",
       text: "#1F2937",
     },
-    asset_image_urls: theme?.asset_image_urls || {},
+    asset_image_urls: theme?.asset_image_urls
+      ? { ...theme.asset_image_urls }
+      : {},
     fonts: theme?.fonts || { heading: "Inter", body: "Inter" },
     is_active: theme?.is_active !== undefined ? theme.is_active : true,
   });
@@ -77,6 +79,11 @@ export function EventThemeForm({ theme, mode }: ThemeFormProps) {
       value,
     })),
   );
+  useEffect(() => {
+    if (mode === "edit" && theme?.asset_image_urls) {
+      console.log("Theme assets loaded:", theme.asset_image_urls);
+    }
+  }, [theme, mode]);
 
   // Submission state
   const [isSubmitting, setIsSubmitting] = useState(false);
@@ -124,7 +131,11 @@ export function EventThemeForm({ theme, mode }: ThemeFormProps) {
 
   // Handle asset images change
   const handleAssetImagesChange = (assets: Record<string, string>) => {
-    setFormState((prev) => ({ ...prev, asset_image_urls: assets }));
+    setFormState((prev) => ({
+      ...prev,
+      // Merge with existing assets rather than replacing
+      asset_image_urls: { ...prev.asset_image_urls, ...assets },
+    }));
   };
 
   // Add a new color input