Allow register to link existing Meshkee accounts after acknowledgement.

Adds optional acknowledgeExistingAccount and documents the CELL_EXISTS_OTHER_SITE → SMS link flow for storefronts.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/auth/auth.service.ts

@@ -79,7 +79,7 @@ export class AuthService {
         existingUser.passwordHash,
       );
 
-      if (!passwordValid) {
+      if (!passwordValid && !dto.acknowledgeExistingAccount) {
         const otherNames = existingUser.businessCustomers
           .map((item) => item.business.nameFa?.trim() || item.business.name)
           .filter(Boolean);