feat: add newsletter service for subscription functionality

This service was missing from the repository, causing build failures.

services/newsletter.service.ts

@@ -0,0 +1,52 @@
+import { api } from './api';
+import { API_ENDPOINTS } from '@/utils/constants';
+
+export interface NewsletterSubscribeData {
+  email: string;
+}
+
+export interface ApiResponse<T = any> {
+  success: boolean;
+  message?: string;
+  data?: T;
+  count?: number;
+}
+
+export const newsletterService = {
+  // Subscribe to newsletter
+  subscribe: async (data: NewsletterSubscribeData): Promise<ApiResponse> => {
+    // Newsletter subscription doesn't require authentication
+    const response = await api.post<ApiResponse>(
+      API_ENDPOINTS.NEWSLETTER.SUBSCRIBE,
+      data,
+      { token: '' } // No token needed for public endpoint
+    );
+    return response;
+  },
+
+  // Unsubscribe from newsletter
+  unsubscribe: async (email: string): Promise<ApiResponse> => {
+    const response = await api.post<ApiResponse>(
+      API_ENDPOINTS.NEWSLETTER.UNSUBSCRIBE,
+      { email },
+      { token: '' } // No token needed for public endpoint
+    );
+    return response;
+  },
+
+  // Get all subscribers (Admin only)
+  getSubscribers: async (): Promise<ApiResponse> => {
+    const response = await api.get<ApiResponse>(
+      API_ENDPOINTS.NEWSLETTER.SUBSCRIBERS
+    );
+    return response;
+  },
+
+  // Get active subscriber count (Admin only)
+  getActiveCount: async (): Promise<number> => {
+    const response = await api.get<ApiResponse>(
+      API_ENDPOINTS.NEWSLETTER.COUNT
+    );
+    return response.count || 0;
+  },
+};