fix(frontend): chat list shows its chats on the first load again

frontend/src/lib/stores/chats.svelte.ts

@@ -35,7 +35,7 @@ function bucketKey(folderId: number | null): string {
 function createChats() {
   let buckets = $state<Record<string, Bucket>>({});
   let extra = $state<Record<number, Chat>>({});
-  let account: number | null = null;
+  let account = $state<number | null>(null);
   const enriched = new Set<number>();
   const resolving = new Set<number>();