feat(client-portal) : phase 3 — ticket notifications

LST-69 (3.2) phase 3. Wires the existing notification system to client-ticket
events (the bell/useNotifications/endpoints already existed).

- Notification.relatedTicket (ManyToOne ClientTicketInterface, SET NULL) +
  additive migration + notification:read group.
- NotifierInterface::notify() gains a backward-compatible optional
  relatedTicket param (existing callers unchanged).
- ClientTicketNumberProcessor (POST): notifies all ROLE_ADMIN users
  (ticket_created), tolerant try/catch after flush. ClientTicketStatusProcessor
  (PATCH): notifies submittedBy on status change (ticket_status_changed).
- Front: notification DTO relatedTicket; NotificationBell navigates to /admin
  (admin) or /portal (client) on ticket notifications.

180 tests green (178 + 2), nuxt build passes, cs-fixer clean.

frontend/services/dto/notification.ts

@@ -7,6 +7,7 @@ export type Notification = {
     type: NotificationType
     title: string
     message: string
+    relatedTicket: string | null
     isRead: boolean
     createdAt: string
 }