feat(npa): add Export to Excel across all 9 NPA reports

Every report screen (Interest, Status, Recovery, Summary, Account Detail,
Movement, Provision, Probable NPA, SMA) now has an Export to Excel button
that builds a workbook from the same derived getters the on-screen tables
use, reusing the shared cashier-export.ts builder.

src/app/npa/npa-reports/npa-reports.component.html

@@ -38,6 +38,9 @@
         <input type="text" [(ngModel)]="asOnDate" placeholder="DD-MM-YYYY" />
       </label>
       <button type="button" class="pg-btn pg-btn--primary" (click)="generate()">Generate</button>
+      <button type="button" class="pg-btn pg-btn--ghost" [disabled]="generating" (click)="exportExcel()">
+        {{ generating ? 'Exporting…' : 'Export to Excel' }}
+      </button>
     </div>
   </header>