feat(tenders): add Tender Management module (SRS, backend, frontend)

- SRS document: docs/SRS_TENDER_MANAGEMENT.md
- Prisma: Tender, TenderDirective models; Deal.sourceTenderId; Attachment.tenderId/tenderDirectiveId
- Backend: tenders module (CRUD, duplicate check, directives, notifications, file upload, convert-to-deal)
- Frontend: tenders list, detail, create/edit forms, directives, convert to deal, i18n (en/ar), dashboard card
- Seed: tenders permissions for admin and sales positions
- Auth: admin.service findFirst for email check (Prisma compatibility)

Made-with: Cursor

backend/src/modules/admin/admin.service.ts

@@ -148,7 +148,7 @@ class AdminService {
       throw new AppError(400, 'هذا الموظف مرتبط بحساب مستخدم بالفعل - Employee already has a user account');
     }
 
-    const emailExists = await prisma.user.findUnique({
+    const emailExists = await prisma.user.findFirst({
       where: { email: data.email },
     });
     if (emailExists) {
@@ -206,7 +206,7 @@ class AdminService {
     }
 
     if (data.email && data.email !== existing.email) {
-      const emailExists = await prisma.user.findUnique({ where: { email: data.email } });
+      const emailExists = await prisma.user.findFirst({ where: { email: data.email } });
       if (emailExists) {
         throw new AppError(400, 'البريد الإلكتروني مستخدم بالفعل - Email already in use');
       }