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/FileCard.jsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react';
 import { useTranslation } from 'react-i18next';
-import { CircleNotch, DownloadSimple, CheckCircle, WarningCircle } from '@phosphor-icons/react';
+import { CircleNotch, DownloadSimple, CheckCircle, WarningCircle, X } from '@phosphor-icons/react';
 import { fetchJobStatus, downloadUrl } from './api.js';
 import { formatBytes } from './utils/formatBytes.js';
 import { fileTypeMeta } from './utils/fileFamily.js';
@@ -9,7 +9,7 @@ function extensionOf(fileName) {
   return fileName.split('.').pop();
 }
 
-export function FileCard({ fileName, fileSize, targetFormat, jobId, initialError }) {
+export function FileCard({ fileName, fileSize, targetFormat, jobId, initialError, onRemove }) {
   const { t } = useTranslation();
   const [status, setStatus] = useState(initialError ? 'failed' : 'pending');
   const [errorMessage, setErrorMessage] = useState(initialError ?? null);
@@ -45,6 +45,14 @@ export function FileCard({ fileName, fileSize, targetFormat, jobId, initialError
         <span className="file-tile-name">{fileName}</span>
         {targetFormat && <span className="format-badge">{targetFormat.toUpperCase()}</span>}
         <span className="file-tile-size">{formatBytes(fileSize)}</span>
+        <button
+          type="button"
+          className="file-remove-button"
+          onClick={onRemove}
+          aria-label={t('common.remove')}
+        >
+          <X size={16} weight="bold" />
+        </button>
       </div>
       {(status === 'pending' || status === 'processing') && (
         <div className="job-progress">