feat: SMTP config en DB, historial mensajes, JWT 90d, email OTP con Prisma

- schema.prisma: modelo message_logs (channel, recipient, body, status, error)
- email-otp.service.ts: lee config SMTP desde DB (settings.smtp_config), registra log en message_logs
- sms.service.ts: registra log en message_logs tras cada envío (éxito y error)
- auth.module.ts: agrega PrismaModule, JWT expira en 90d
- settings.controller.ts: GET/PATCH /settings/smtp + GET /settings/message-logs
- settings.service.ts: método getMessageLogs con paginación y filtro por canal
- settings.module.ts: importa AuthModule + EmailOtpService

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

backend/prisma/schema.prisma

@@ -192,6 +192,16 @@ model suggestions {
   created_at DateTime @default(now()) @db.Timestamptz(6)
 }
 
+model message_logs {
+  id         String   @id @default(dbgenerated("uuid_generate_v4()")) @db.Uuid
+  channel    String   @db.VarChar(10)  // 'sms' | 'email'
+  recipient  String   @db.VarChar(255)
+  body       String
+  status     String   @db.VarChar(20)  // 'sent' | 'error'
+  error      String?
+  created_at DateTime @default(now()) @db.Timestamptz(6)
+}
+
 model specializations {
   id              String        @id @default(dbgenerated("uuid_generate_v4()")) @db.Uuid
   professional_id String        @db.Uuid