feat: version 4.6.0 -- Cambio de correo con aprobacion

El usuario solicita el cambio desde Mi cuenta (correo nuevo + clave actual). Lo
aprueba un admin/superadmin (colaboradores), solo un superadmin (admins) o el propio
superadmin mediante enlace a su correo actual. Tras aprobar se envia confirmacion al
correo nuevo y aviso al actual; al confirmar se aplica el cambio y se cierran todas
las sesiones. Todo el proceso queda en auditoria. Migracion 035.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/i18n/messages.js

@@ -1,5 +1,6 @@
 export const messages = {
   'es-EC': {
+    email_change_title: 'Cambiar correo', email_change_new: 'Correo nuevo', email_change_request: 'Solicitar cambio', email_change_requested: 'Solicitud creada', email_change_cancel: 'Cancelar solicitud', email_change_cancelled: 'Solicitud cancelada', email_change_requests: 'Solicitudes de cambio de correo', email_change_none: 'No hay solicitudes pendientes', email_change_approve: 'Aprobar', email_change_reject: 'Rechazar', email_change_reason: 'Motivo del rechazo', email_change_approved: 'Cambio aprobado', email_change_rejected: 'Cambio rechazado', email_change_approve_title: 'Aprobar mi cambio de correo', email_change_confirm_title: 'Confirmar correo nuevo', email_change_accept: 'Aceptar', email_change_self_approved: 'Aprobado. Revisa el correo nuevo para confirmarlo.', email_change_applied: 'Correo actualizado. Todas tus sesiones se cerraron. Inicia sesión con:', email_change_status_pending: 'Pendiente de aprobación', email_change_status_approved: 'Aprobada: revisa tu correo nuevo', email_change_status_rejected: 'Rechazada', email_change_status_cancelled: 'Cancelada', email_change_status_expired: 'Vencida', email_change_status_failed: 'Fallida', email_change_status_applied: 'Aplicada',
     nav_calendar: 'Calendario',
     calendar_date: 'Fecha',
     notification_meeting_created: 'Nueva reunión', notification_meeting_updated: 'Reunión modificada', notification_meeting_cancelled: 'Reunión cancelada', notification_meeting_occurrence_cancelled: 'Ocurrencia cancelada', notification_meeting_reminder: 'Recordatorio de reunión', notification_meeting_rsvp_accepted: 'Aceptó la reunión', notification_meeting_rsvp_declined: 'Rechazó la reunión', notification_meeting_rsvp_tentative: 'Respondió quizás',
@@ -625,6 +626,7 @@ export const messages = {
     notifications_mark_all_read: 'Marcar todas como leidas',
   },
   'en-US': {
+    email_change_title: 'Change email', email_change_new: 'New email', email_change_request: 'Request change', email_change_requested: 'Request created', email_change_cancel: 'Cancel request', email_change_cancelled: 'Request cancelled', email_change_requests: 'Email change requests', email_change_none: 'No pending requests', email_change_approve: 'Approve', email_change_reject: 'Reject', email_change_reason: 'Rejection reason', email_change_approved: 'Change approved', email_change_rejected: 'Change rejected', email_change_approve_title: 'Approve my email change', email_change_confirm_title: 'Confirm new email', email_change_accept: 'Accept', email_change_self_approved: 'Approved. Check your new email to confirm it.', email_change_applied: 'Email updated. All sessions were closed. Sign in with:', email_change_status_pending: 'Pending approval', email_change_status_approved: 'Approved: check your new email', email_change_status_rejected: 'Rejected', email_change_status_cancelled: 'Cancelled', email_change_status_expired: 'Expired', email_change_status_failed: 'Failed', email_change_status_applied: 'Applied',
     nav_calendar: 'Calendar',
     calendar_date: 'Date',
     notification_meeting_created: 'New meeting', notification_meeting_updated: 'Meeting updated', notification_meeting_cancelled: 'Meeting cancelled', notification_meeting_occurrence_cancelled: 'Occurrence cancelled', notification_meeting_reminder: 'Meeting reminder', notification_meeting_rsvp_accepted: 'Accepted meeting', notification_meeting_rsvp_declined: 'Declined meeting', notification_meeting_rsvp_tentative: 'Replied maybe',