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.

hooks/usePreferences.ts

@@ -5,6 +5,7 @@ interface Preferences {
   homeBackground: string | null;
   eventsBackground: string | null;
   leaderboardBackground: string | null;
+  challengesBackground: string | null;
 }
 
 export function usePreferences() {
@@ -21,6 +22,7 @@ export function usePreferences() {
             homeBackground: null,
             eventsBackground: null,
             leaderboardBackground: null,
+            challengesBackground: null,
           }
         );
         setLoading(false);
@@ -30,6 +32,7 @@ export function usePreferences() {
           homeBackground: null,
           eventsBackground: null,
           leaderboardBackground: null,
+          challengesBackground: null,
         });
         setLoading(false);
       });
@@ -39,7 +42,7 @@ export function usePreferences() {
 }
 
 export function useBackgroundImage(
-  page: "home" | "events" | "leaderboard",
+  page: "home" | "events" | "leaderboard" | "challenges",
   defaultImage: string
 ) {
   const { preferences } = usePreferences();