feat: add app header, sidebar, and mobile navigation components

- Implemented AppHeader component with theme toggle and connection status.
- Created AppSidebar component for navigation with connection status indicator.
- Added MobileNav component for mobile navigation with responsive design.
- Introduced shared components: DetailStat, EmptyState, ErrorState, LoadingSkeleton, and StatCard for consistent UI.
- Developed hooks for async data fetching: useAsync, useConfig, useDashboard, useGuilds, useMedia, useMessages, useRecordings, and useVoice.
- Added chatbot API functions for sending messages and managing chat history.

services/frontend/src/lib/api/chatbot.ts

@@ -0,0 +1,11 @@
+import type { ChatbotResponse, ChatHistoryMessage } from "@/lib/types";
+import { api } from "./client";
+
+export const chatbotApi = {
+  send: (message: string) =>
+    api.post<ChatbotResponse>("/api/mascot/chat", { message }),
+
+  getHistory: () => api.get<ChatHistoryMessage[]>("/api/mascot/chat/history"),
+
+  clearHistory: () => api.delete<{ ok: boolean }>("/api/mascot/chat/history"),
+};