Add performance optimizations and component refactors

- Cache read-heavy public API routes via redisCache (leaderboard, values,
  shop, articles, photos, guilds, teams, staff, users, home, radio, badges)
- Add single-flight and bounded-memory cache layer with unit tests
- Parallelize independent DB queries on search, rares, shop, staff, polls
  and profile pages
- Push radio points leaderboard aggregation to SQL with a LIMIT
- Split studio-client and import-furni-client into focused modules
- Clean up next.config.ts

src/lib/redis-cache.ts

@@ -20,3 +20,17 @@ export async function redisCache<T>(
 export function apiCacheKey(path: string): string {
 	return `api:${path}`;
 }
+
+/**
+ * Deep-convert a payload to a JSON-cache-safe form: BigInt → string (matching
+ * the apiJson() wire format) and Date → ISO string, since JSON.stringify throws
+ * on BigInt. Use for payloads cached through redisCache() that are serialised
+ * straight to a response and never consumed by page logic.
+ */
+export function cacheSafe<T>(value: T): T {
+	return JSON.parse(
+		JSON.stringify(value, (_k, v) =>
+			typeof v === "bigint" ? v.toString() : v,
+		),
+	) as T;
+}