fix: nominee share & joint ownership validation across all account types

- Block 0% nominee share in all steppers (Savings, FD, RD, Current) —
  Add button disabled via isValid, addNominee() guards < 1, nominee-form
  error condition fixed for value=0
- Joint ownership: default primary share 50%, enforce min 1% on blur,
  max 100% on input with DOM clamp via $event, auto-redistribute
  co-holders proportionally when primary share changes,
  isJointOwnershipValid guards each holder >= 1
- Pending/Rejected account tabs: normalize date format to 22 May 2026
  for both array and string date values from API

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/shared/nominee-form/nominee-form.component.html

@@ -162,8 +162,12 @@
           <mat-form-field appearance="outline" class="nom-field-item nom-field-item--sm">
             <mat-label>Share %</mat-label>
             <input matInput type="number" [(ngModel)]="percentageShare" min="1" max="100" />
-            @if (percentageShare && (percentageShare < 1 || percentageShare > 100)) {
-              <mat-error>1–100</mat-error>
+            @if (
+              percentageShare !== null &&
+              percentageShare !== undefined &&
+              (percentageShare < 1 || percentageShare > 100)
+            ) {
+              <mat-error>Share must be 1–100%</mat-error>
             }
           </mat-form-field>