refactor(data): add mock API adapters, id utility, and toast feedback

lib/api/chat.ts

@@ -0,0 +1,13 @@
+import { useChatStore } from "@/store/chat"
+
+export function listChatSessions() {
+  return useChatStore.getState().sessions
+}
+
+export function getChatSessionById(sessionId: string) {
+  return useChatStore.getState().sessions.find((session) => session.id === sessionId)
+}
+
+export function listChatMessages(sessionId: string) {
+  return useChatStore.getState().messages.filter((message) => message.sessionId === sessionId)
+}