feat(admin): visual theme cards, album search, and status dashboard (#241)

* feat(admin): implement visual theme cards, album search, and system status diagnostics

* fix(admin): resolve type-checking build errors in SettingsEditor and status route

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Co-authored-by: ralksta <ralksta@users.noreply.github.com>

lib/cache.ts

@@ -12,6 +12,10 @@ class MemoryCache {
   private store = new Map<string, CacheEntry<unknown>>();
   private maxEntries = 200;
 
+  get size(): number {
+    return this.store.size;
+  }
+
   get<T>(key: string): T | null {
     const entry = this.store.get(key);
     if (!entry) return null;