rename frontend subfolder

frontend/src/lib/router.svelte.js

@@ -0,0 +1,31 @@
+import { chatStore } from "./chatStore.svelte.js";
+
+// keyed by chat_id → chatStore instance
+const cache = $state({});
+
+// which chat is on screen right now
+export const activeChatId = $state(null);
+
+export function getStore(chatId) {
+  if (!cache[chatId]) {
+    cache[chatId] = chatStore(chatId);
+  }
+  return cache[chatId];
+}
+
+export function switchChat(chatId) {
+  activeChatId = chatId;
+}
+
+export function newChat() {
+  const id = "chat_" + crypto.randomUUID();
+  switchChat(id);
+  return id;
+}
+
+// restore last opened chat (or create first one)
+(() => {
+  const ids = JSON.parse(localStorage.getItem("chat_ids") || "[]");
+  if (ids.length) switchChat(ids[0]);
+  else newChat();
+})();