feat(email): read-only "Sent emails" tab over email_queue

Add a paginated, filterable view of the email_queue (recipient, type,
status, queued/sent timestamps, error, event link) as a third tab in
Email config, beside SMTP + Templates. Filters: status, recipient/type
search, created-at range. email_data is never exposed. Pairs with the
"Send queued emails now" flush — flush, then watch what sent/failed.

frontend/src/services/email.service.ts

@@ -1,5 +1,27 @@
 import { api } from '../config/api';
 
+export type EmailQueueStatus = 'pending' | 'sent' | 'failed';
+
+export interface EmailQueueItem {
+  id: number;
+  recipientEmail: string;
+  emailType: string;
+  status: EmailQueueStatus;
+  createdAt: string;
+  scheduledAt: string | null;
+  sentAt: string | null;
+  errorMessage: string | null;
+  retryCount: number;
+  eventId: number | null;
+  eventName: string | null;
+  eventSlug: string | null;
+}
+
+export interface EmailQueueListResponse {
+  items: EmailQueueItem[];
+  pagination: { total: number; page: number; pageSize: number; totalPages: number };
+}
+
 export interface EmailConfig {
   smtp_host: string;
   smtp_port: number;
@@ -84,6 +106,21 @@ export const emailService = {
     return response.data;
   },
 
+  /** Read-only "Sent emails" feed — paginated view of the email_queue
+   *  table with filters. email_data is never returned. */
+  async listQueue(params: {
+    status?: EmailQueueStatus;
+    emailType?: string;
+    q?: string;
+    from?: string;
+    to?: string;
+    page?: number;
+    pageSize?: number;
+  } = {}): Promise<EmailQueueListResponse> {
+    const response = await api.get<EmailQueueListResponse>('/admin/email/queue', { params });
+    return response.data;
+  },
+
   // Get all email templates
   async getTemplates(): Promise<EmailTemplate[]> {
     const response = await api.get<EmailTemplate[]>('/admin/email/templates');