Add challenges background preference support: Extend site preferences and related components to include challengesBackground, update API and UI to handle new background image settings for challenges.

actions/admin/preferences.ts

@@ -19,6 +19,7 @@ export async function updateSitePreferences(data: {
   homeBackground?: string | null;
   eventsBackground?: string | null;
   leaderboardBackground?: string | null;
+  challengesBackground?: string | null;
 }) {
   try {
     await checkAdminAccess()();
@@ -27,12 +28,14 @@ export async function updateSitePreferences(data: {
       homeBackground: data.homeBackground,
       eventsBackground: data.eventsBackground,
       leaderboardBackground: data.leaderboardBackground,
+      challengesBackground: data.challengesBackground,
     });
 
     revalidatePath("/admin");
     revalidatePath("/");
     revalidatePath("/events");
     revalidatePath("/leaderboard");
+    revalidatePath("/challenges");
 
     return { success: true, data: preferences };
   } catch (error) {