feat: visual polish & UX — fade-in, theme toggle, scroll-to-top, footer, cursor, badge

- Add FadeIn component (IntersectionObserver scroll-reveal + load animation)
- Add dark/light theme toggle (useSyncExternalStore + localStorage)
- Add scroll-to-top button (appears after 300px scroll)
- Add configurable footer with social links (gallery.yaml)
- Add crosshair cursor on photo grid items
- Add 'X photos' count badge on subpage cover images
- Add light theme color palette in tokens.css

lib/cache.ts

@@ -4,42 +4,42 @@
  */
 
 interface CacheEntry<T> {
-    data: T;
-    expiresAt: number;
+  data: T;
+  expiresAt: number;
 }
 
 class MemoryCache {
-    private store = new Map<string, CacheEntry<unknown>>();
-    private maxEntries = 200;
+  private store = new Map<string, CacheEntry<unknown>>();
+  private maxEntries = 200;
 
-    get<T>(key: string): T | null {
-        const entry = this.store.get(key);
-        if (!entry) return null;
+  get<T>(key: string): T | null {
+    const entry = this.store.get(key);
+    if (!entry) return null;
 
-        if (Date.now() > entry.expiresAt) {
-            this.store.delete(key);
-            return null;
-        }
-
-        return entry.data as T;
+    if (Date.now() > entry.expiresAt) {
+      this.store.delete(key);
+      return null;
     }
 
-    set<T>(key: string, data: T, ttlMs: number): void {
-        // Evict oldest entries if at capacity
-        if (this.store.size >= this.maxEntries) {
-            const firstKey = this.store.keys().next().value;
-            if (firstKey) this.store.delete(firstKey);
-        }
+    return entry.data as T;
+  }
 
-        this.store.set(key, {
-            data,
-            expiresAt: Date.now() + ttlMs,
-        });
+  set<T>(key: string, data: T, ttlMs: number): void {
+    // Evict oldest entries if at capacity
+    if (this.store.size >= this.maxEntries) {
+      const firstKey = this.store.keys().next().value;
+      if (firstKey) this.store.delete(firstKey);
     }
 
-    clear(): void {
-        this.store.clear();
-    }
+    this.store.set(key, {
+      data,
+      expiresAt: Date.now() + ttlMs,
+    });
+  }
+
+  clear(): void {
+    this.store.clear();
+  }
 }
 
 export const cache = new MemoryCache();