fix(clients): block Alternate Mobile No from matching Mobile No

Same number in both fields defeats the point of having a second contact
route, and re-running DIP on an identical number is pointless. Added a
cross-field validator on alternateMobileNo, re-checked whenever mobileNo
changes, with a matching error message and the Verify-with-DIP button
disabled while the clash exists.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/clients/client-stepper/client-general-step/client-general-step.component.html

@@ -969,6 +969,11 @@
           createClientForm.get('alternateMobileNo')?.touched
         ) {
           <mat-error>Enter valid 10-digit number (starts with 6-9)</mat-error>
+        } @else if (
+          createClientForm.get('alternateMobileNo')?.hasError('sameAsMobile') &&
+          createClientForm.get('alternateMobileNo')?.touched
+        ) {
+          <mat-error>Alternate number can't be the same as Mobile No</mat-error>
         }
       </mat-form-field>
 
@@ -979,7 +984,11 @@
             color="primary"
             type="button"
             class="verify-btn"
-            [disabled]="readOnly || createClientForm.get('alternateMobileNo')?.value?.length !== 10"
+            [disabled]="
+              readOnly ||
+              createClientForm.get('alternateMobileNo')?.value?.length !== 10 ||
+              createClientForm.get('alternateMobileNo')?.hasError('sameAsMobile')
+            "
             (click)="verifyAlternateDIP()"
           >
             <fa-icon icon="shield-alt" class="m-r-10"></fa-icon>