feat(auth): one mobile, one person across sales experts and customers

Experts (AdminUser) and customers (Customer) sign in to the same apps by mobile
but live in different tables, so the database cannot make the number unique
across them. A number could be given to an expert and to a customer, and the
login then silently merged the two (the customer row was adopted as the expert's
trading account), which left the expert on a customer session and the panel's
name edits unreachable.

The reference rejected a duplicate at entry (`unique:customers`, the agent being
a customers row too); this does the same where a number is typed in:

- customer create/update (wholesale, banker, walk-in): refused when an ACTIVE
  expert holds the number;
- expert create/update: refused when a customer holds it (the expert's own
  trading account excepted);
- the app's self sign-up: refused when an active expert holds it.

Only a number being created or CHANGED is checked, so existing duplicates keep
signing in and stay editable; the login's "expert wins" adoption is untouched.
Plain equality on the two unique columns, normalised with faToEn, so both
lookups are index hits.

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

apps/api/src/modules/customer-auth/customer-auth.service.ts

@@ -28,6 +28,7 @@ import { CUSTOMER_TOKEN_TYPE, EXPERT_TOKEN_TYPE, type CustomerJwtPayload } from
 import { faToEn } from './digits';
 import { SmsService } from '../sms/sms.service';
 import { brandName } from '../../common/brand';
+import { activeExpertHoldsMobile } from '../../common/mobile-owner';
 import type { RegisterDto } from './dto/register.dto';
 
 /** Nest 10 has no TooManyRequestsException; 429 with a Persian message. */
@@ -235,7 +236,7 @@ export class CustomerAuthService {
     const fname = dto.fname.trim();
     const lname = dto.lname.trim();
     const existing = await this.prisma.customer.findUnique({ where: { mobile }, select: { id: true } });
-    if (existing) {
+    if (existing || (await activeExpertHoldsMobile(this.prisma, mobile))) {
       throw new ConflictException('این شماره موبایل قبلاً ثبت شده است. از بخش ورود وارد شوید.');
     }