FX-5: scan-ingestion UI on the marking page

The marking flow read student_submissions but there was no way to create them —
print→scan→mark could not be completed in-app. Add an "Upload scans" control to
the marking queue that posts PDFs to the existing POST /batches/{id}/scans and
refreshes the queue.

- examRepository.uploadScan(batchId, file, {studentId?, matchingMethod?}): multipart
  upload (axios sets the boundary), returns the created/updated StudentSubmission.
- ExamMarkingPage: "Upload scans" button + hidden multi-file PDF input; uploads each
  with matching_method='ordered' (fills the roster in order; unmatched scans become
  reconcilable submissions), then reloads the queue with a success/failure summary.

No API or schema change (endpoint already existed). tsc clean; behaviour is covered
by the cc-browser-tester card (FX-V).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/services/exam/examRepository.ts

@@ -28,6 +28,7 @@ import type {
   Neo4jSyncResult,
   PatchQuestionPayload,
   SpecPoint,
+  StudentSubmission,
   TemplateReplacePayload,
   UpdateTemplateMetaPayload,
 } from '../../types/exam.types';
@@ -298,6 +299,21 @@ export const examRepository = {
     const res = await axios.put(`${EXAM_BASE}/marks/${markId}`, payload, { headers });
     return res.data;
   },
+
+  async uploadScan(
+    batchId: string,
+    file: File,
+    opts: { studentId?: string; matchingMethod?: 'manual' | 'ordered' } = {},
+  ): Promise<StudentSubmission> {
+    const headers = await authHeaders();
+    const form = new FormData();
+    form.append('file', file);
+    form.append('matching_method', opts.matchingMethod ?? 'ordered');
+    if (opts.studentId) form.append('student_id', opts.studentId);
+    // Let axios set the multipart Content-Type + boundary (only Authorization is forwarded).
+    const res = await axios.post<StudentSubmission>(`${EXAM_BASE}/batches/${batchId}/scans`, form, { headers });
+    return res.data;
+  },
 };
 
 export default examRepository;