Exam bank: corpus coverage dashboard (/exam-marker/corpus)

New "Exam bank" page displaying the state of the collected past-paper corpus:
per-specification coverage of question papers / mark schemes / examiner reports,
with global + filtered rollups, board/level/subject filters, a "sciences only"
default, and an expandable per-session table (QP/MS/ER present ✓/–). Reads
GET /api/exam/corpus. Dashboard gets an "Exam bank" entry point.

examRepository.getCorpus + corpus types. tsc clean on the changed files.

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

src/services/exam/examRepository.ts

@@ -14,6 +14,7 @@ import type {
   AutoMapJobStatus,
   AutoMapResponse,
   BankResponse,
+  CorpusResponse,
   BatchQueueResponse,
   BatchResultsResponse,
   CreateBatchPayload,
@@ -303,6 +304,12 @@ export const examRepository = {
     return res.data;
   },
 
+  async getCorpus(): Promise<CorpusResponse> {
+    const headers = await authHeaders();
+    const res = await axios.get<CorpusResponse>(`${EXAM_BASE}/corpus`, { headers });
+    return res.data;
+  },
+
   async getBank(params: { specRef?: string; subject?: string } = {}): Promise<BankResponse> {
     const headers = await authHeaders();
     const res = await axios.get<BankResponse>(`${EXAM_BASE}/bank`, {