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.ts

@@ -25,7 +25,10 @@ import {
   UntypedFormGroup,
   Validators,
   UntypedFormControl,
-  ReactiveFormsModule
+  ReactiveFormsModule,
+  ValidatorFn,
+  AbstractControl,
+  ValidationErrors
 } from '@angular/forms';
 import { Subject, Subscription, merge } from 'rxjs';
 import { filter, switchMap, takeUntil } from 'rxjs/operators';
@@ -922,6 +925,16 @@ export class ClientGeneralStepComponent implements OnInit, OnDestroy, OnChanges
     }
   }
 
+  /** Alternate Mobile No must differ from Mobile No — the same number saved in both fields is
+   *  meaningless (there's no second contact route) and the DIP checks would just repeat. */
+  private notSameAsMobileNoValidator(): ValidatorFn {
+    return (control: AbstractControl): ValidationErrors | null => {
+      const value = control.value;
+      const mobileNo = control.parent?.get('mobileNo')?.value;
+      return value && mobileNo && value === mobileNo ? { sameAsMobile: true } : null;
+    };
+  }
+
   /**
    * Creates the client form.
    */
@@ -961,7 +974,8 @@ export class ClientGeneralStepComponent implements OnInit, OnDestroy, OnChanges
         '',
         [
           Validators.pattern(/^[6-9]\d{9}$/),
-          Validators.maxLength(10)
+          Validators.maxLength(10),
+          this.notSameAsMobileNoValidator()
         ]
       ],
       emailAddress: [
@@ -1334,6 +1348,10 @@ export class ClientGeneralStepComponent implements OnInit, OnDestroy, OnChanges
         // invalid) and its own reset never had a chance to run.
         this.mobileOtpVerified = false;
         this.mobileNewOtpId = null;
+        // Alternate Mobile No's "not same as Mobile No" validator reads mobileNo's current
+        // value, so re-run it here too — otherwise fixing mobileNo away from a clash leaves
+        // the alternate field's error stuck until the user also edits that field.
+        this.createClientForm.get('alternateMobileNo')?.updateValueAndValidity({ emitEvent: false });
       });
 
     this.createClientForm