Refactor admin preferences management to use global site preferences, update UI components for better user experience, and implement image selection for background settings.

prisma/migrations/20251209073256_add_site_preferences/migration.sql

@@ -0,0 +1,9 @@
+-- CreateTable
+CREATE TABLE "SitePreferences" (
+    "id" TEXT NOT NULL PRIMARY KEY DEFAULT 'global',
+    "homeBackground" TEXT,
+    "eventsBackground" TEXT,
+    "leaderboardBackground" TEXT,
+    "createdAt" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" DATETIME NOT NULL
+);