perf(api,frontend): index hot queries, paginate chats, fix realtime

frontend/src/lib/stores/chat-picker.svelte.ts

@@ -0,0 +1,42 @@
+import { listChats } from "$lib/api/endpoints";
+import type { Chat } from "$lib/api/types";
+
+const DEBOUNCE_MS = 250;
+const LIMIT = 40;
+
+export function createChatPicker() {
+  let results = $state<Chat[]>([]);
+  let timer: ReturnType<typeof setTimeout> | null = null;
+  let seq = 0;
+
+  async function run(query: string, current: number) {
+    try {
+      const found = await listChats({
+        limit: LIMIT,
+        search: query || undefined,
+      });
+      if (current === seq) {
+        results = found;
+      }
+    } catch {
+      if (current === seq) {
+        results = [];
+      }
+    }
+  }
+
+  return {
+    get results(): Chat[] {
+      return results;
+    },
+    search(query: string) {
+      const current = ++seq;
+      if (timer !== null) {
+        clearTimeout(timer);
+      }
+      timer = setTimeout(() => {
+        run(query.trim(), current).catch(() => undefined);
+      }, DEBOUNCE_MS);
+    },
+  };
+}