Add SMTP test email endpoint and mail logs in admin settings

- POST /settings/test-email: send test email to diagnose SMTP config
- Admin settings: test email form + last 20 email logs with status/error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/settings/settings.controller.ts

@@ -1,14 +1,15 @@
-import { Controller, Get, Patch, Body, UseGuards, Param, Res, Query } from '@nestjs/common';
+import { Controller, Get, Post, Patch, Body, UseGuards, Param, Res, Query } from '@nestjs/common';
 import { ApiTags, ApiBearerAuth } from '@nestjs/swagger';
 import { Response } from 'express';
 import { SettingsService } from './settings.service';
 import { JwtAuthGuard } from '../auth/jwt-auth.guard';
 import { EmailOtpService } from '../auth/email-otp.service';
+import { MailService } from '../mail/mail.service';
 
 @ApiTags('Settings')
 @Controller('settings')
 export class SettingsController {
-  constructor(private settings: SettingsService, private emailOtp: EmailOtpService) {}
+  constructor(private settings: SettingsService, private emailOtp: EmailOtpService, private mail: MailService) {}
 
   @Get()
   getGlobal() { return this.settings.getGlobal(); }
@@ -44,6 +45,21 @@ export class SettingsController {
     return this.emailOtp.saveSmtpConfig(body);
   }
 
+  @Post('test-email')
+  @UseGuards(JwtAuthGuard) @ApiBearerAuth()
+  async testEmail(@Body() body: { to: string }) {
+    await this.mail.tryMail(
+      body.to,
+      'Correo de prueba — ProsApp',
+      `<div style="font-family:sans-serif;padding:32px;max-width:480px;margin:auto">
+        <h2 style="color:#1e293b">✅ Configuración SMTP correcta</h2>
+        <p style="color:#64748b">Si recibes este correo, el servidor SMTP está funcionando correctamente en ProsApp.</p>
+        <p style="color:#94a3b8;font-size:12px">Enviado desde el panel de administración.</p>
+      </div>`,
+    );
+    return { message: `Correo de prueba enviado a ${body.to}` };
+  }
+
   // Message logs
   @Get('message-logs')
   @UseGuards(JwtAuthGuard) @ApiBearerAuth()