Refactor monolithic modules and harden booking, email, and auth infrastructure.

Split oversized frontend API client, email service, and admin/booking pages into focused modules while preserving import surfaces, and add Redis-backed queues, stale booking cleanup, stronger auth, and scale deployment configs.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/api/users.ts

@@ -0,0 +1,20 @@
+import { fetchApi } from './client';
+import type { User } from './types';
+
+export const usersApi = {
+  getAll: (role?: string) => {
+    const query = role ? `?role=${role}` : '';
+    return fetchApi<{ users: User[] }>(`/api/users${query}`);
+  },
+
+  getById: (id: string) => fetchApi<{ user: User }>(`/api/users/${id}`),
+
+  update: (id: string, data: Partial<User>) =>
+    fetchApi<{ user: User }>(`/api/users/${id}`, {
+      method: 'PUT',
+      body: JSON.stringify(data),
+    }),
+
+  delete: (id: string) =>
+    fetchApi<{ message: string }>(`/api/users/${id}`, { method: 'DELETE' }),
+};