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/hooks/use-config.ts

@@ -0,0 +1,21 @@
+import { configApi } from "@/lib/api";
+import type { AppConfig } from "@/lib/types";
+import { useAsync } from "./use-async";
+
+interface UseConfigReturn {
+  config: AppConfig | null;
+  loading: boolean;
+  error: string | null;
+  refetch: () => void;
+}
+
+/**
+ * Fetch the app configuration from the backend.
+ */
+export function useConfig(): UseConfigReturn {
+  const { data, loading, error, refetch } = useAsync<AppConfig>(
+    () => configApi.get(),
+    [],
+  );
+  return { config: data, loading, error, refetch };
+}