Upload feature (f): demo scenarios (upload-slow/fail) + a11y (file-input label)

- upload-slow/upload-fail scenarios simulated in the adapter (XHR POST bypasses the
  HTTP interceptor); categories/status/delete already honour the global slow/error
- file-input gets a per-category accessible name (aria-label + visible button text)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/ui/upload/document-category/document-category.component.ts

@@ -1,4 +1,4 @@
-import { Component, input, output } from '@angular/core';
+import { Component, computed, input, output } from '@angular/core';
 import type { DeliveryChannel, DocumentCategory, Upload } from '@shared/upload/upload.machine';
 import { DeliveryChannelToggleComponent } from '../delivery-channel-toggle/delivery-channel-toggle.component';
 import { FileInputComponent } from '../file-input/file-input.component';
@@ -42,6 +42,7 @@ import { SingleUploadComponent } from '../single-upload/single-upload.component'
     @if (channel() === 'digital') {
       <app-file-input
         [inputId]="category().categoryId + '-file'"
+        [label]="fileInputLabel()"
         [accept]="category().acceptedTypes"
         [multiple]="category().multiple"
         (filesSelected)="fileSelected.emit($event)" />
@@ -67,6 +68,9 @@ export class DocumentCategoryComponent {
   channel = input.required<DeliveryChannel>();
   rejection = input<string>();
 
+  /** Accessible name for the file picker, e.g. "Bestand kiezen voor Diploma". */
+  protected fileInputLabel = computed(() => $localize`:@@upload.fileInput.labelFor:Bestand kiezen voor ${this.category().label}:category:`);
+
   fileSelected = output<File[]>();
   removeUpload = output<string>();
   retryUpload = output<string>();

src/app/shared/ui/upload/file-input/file-input.component.ts

@@ -30,6 +30,7 @@ import { Component, ElementRef, input, output, viewChild } from '@angular/core';
         #fileInput
         type="file"
         [id]="inputId()"
+        [attr.aria-label]="label()"
         [accept]="accept().join(',')"
         [multiple]="multiple()"
         [disabled]="disabled()"
@@ -38,7 +39,7 @@ import { Component, ElementRef, input, output, viewChild } from '@angular/core';
         class="utrecht-button rhc-button utrecht-button--secondary-action label"
         [class.utrecht-button--disabled]="disabled()">
         <span aria-hidden="true">↑</span>
-        <span i18n="@@upload.fileInput.label">Bestand kiezen</span>
+        <span>{{ label() }}</span>
       </span>
     </span>
   `,
@@ -48,6 +49,8 @@ export class FileInputComponent {
   multiple = input(false);
   disabled = input(false);
   inputId = input.required<string>();
+  /** Accessible name + button text; the domain caller supplies a per-category label. */
+  label = input($localize`:@@upload.fileInput.label:Bestand kiezen`);
 
   filesSelected = output<File[]>();