fix: resolve TypeORM cascade bug in ticket reply/close/updateStatus

- Replace ticketsRepo.save(ticket) with ticketsRepo.update() to avoid
  cascade orphaning existing messages (SET ticketId=null violates NOT NULL)
- Fix reply(), close() in tickets.service.ts
- Fix updateStatus() in tickets.controller.ts using new updateTicketFields() method
- Add updateTicketFields() helper to TicketsService for safe partial updates

backend/src/tickets/tickets.service.ts

@@ -85,24 +85,20 @@ export class TicketsService {
 
   // ─── Reply to ticket ───
   async reply(ticketId: string, userId: string, userRole: UserRole, dto: ReplyTicketDto): Promise<TicketMessage> {
-    const ticket = await this.findOne(ticketId, userId, userRole);
+    // Verify access first
+    await this.findOne(ticketId, userId, userRole);
 
     const msg = this.messagesRepo.create({
-      ticketId: ticket.id,
+      ticketId,
       senderId: userId,
       senderRole: userRole,
       message: dto.message,
     });
     const saved = await this.messagesRepo.save(msg);
 
-    // Update ticket status based on who replied
-    if (userRole === UserRole.USER) {
-      ticket.status = TicketStatus.WAITING;
-    } else {
-      // Staff or admin replied
-      ticket.status = TicketStatus.ANSWERED;
-    }
-    await this.ticketsRepo.save(ticket);
+    // Update ticket status directly (avoid cascade issues with loaded relations)
+    const newStatus = userRole === UserRole.USER ? TicketStatus.WAITING : TicketStatus.ANSWERED;
+    await this.ticketsRepo.update(ticketId, { status: newStatus });
 
     this.logger.log(`Reply on ticket ${ticketId} by ${userRole} user ${userId}`);
     return saved;
@@ -110,10 +106,17 @@ export class TicketsService {
 
   // ─── Close ticket ───
   async close(ticketId: string, userId: string, userRole: UserRole): Promise<Ticket> {
-    const ticket = await this.findOne(ticketId, userId, userRole);
-    ticket.status = TicketStatus.CLOSED;
-    ticket.closedAt = new Date();
-    return this.ticketsRepo.save(ticket);
+    await this.findOne(ticketId, userId, userRole);
+    await this.ticketsRepo.update(ticketId, {
+      status: TicketStatus.CLOSED,
+      closedAt: new Date(),
+    });
+    return this.findOne(ticketId, userId, userRole);
+  }
+
+  // ─── Update ticket fields (safe, no cascade) ───
+  async updateTicketFields(ticketId: string, data: Partial<Ticket>): Promise<void> {
+    await this.ticketsRepo.update(ticketId, data);
   }
 
   // ─── Staff: List department tickets ───