fix: replace non-UUID fallback

lib/utils.ts

@@ -11,7 +11,13 @@ export function generateUUID(): string {
   if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function') {
     return crypto.randomUUID();
   }
-  return `${Date.now()}-${Math.random().toString(36).slice(2, 11)}`;
+  // Fallback: construct a v4 UUID from crypto.getRandomValues
+  const bytes = new Uint8Array(16);
+  crypto.getRandomValues(bytes);
+  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
+  bytes[8] = (bytes[8] & 0x3f) | 0x80; // variant 1
+  const hex = Array.from(bytes, b => b.toString(16).padStart(2, '0')).join('');
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`;
 }
 
 export function formatDate(date: Date | string): string {