feat(frontend): add remove button to pending and submitted file cards

Lets users drop an uploaded file from the UI list before or after
conversion, without cancelling anything server-side.

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

frontend/src/components/FileConfigCard.jsx

@@ -1,3 +1,4 @@
+import { X } from '@phosphor-icons/react';
 import { formatBytes } from '../utils/formatBytes.js';
 import { fileTypeMeta } from '../utils/fileFamily.js';
 
@@ -32,7 +33,7 @@ function RangeField({ label, value, min, max, onChange }) {
   );
 }
 
-export function FileConfigCard({ item, index, t, onTargetFormatChange, onQualityChange, onIconSizeChange }) {
+export function FileConfigCard({ item, index, t, onTargetFormatChange, onQualityChange, onIconSizeChange, onRemove }) {
   const { Icon, colorVar } = fileTypeMeta(extensionOf(item.file.name));
 
   return (
@@ -43,6 +44,14 @@ export function FileConfigCard({ item, index, t, onTargetFormatChange, onQuality
         </span>
         <span className="file-tile-name">{item.file.name}</span>
         <span className="file-tile-size">{formatBytes(item.file.size)}</span>
+        <button
+          type="button"
+          className="file-remove-button"
+          onClick={() => onRemove(index)}
+          aria-label={t('common.remove')}
+        >
+          <X size={16} weight="bold" />
+        </button>
       </div>
 
       {item.targets.length > 0 ? (