Mode-3: Question bank page + custom-paper assembly UI

New /exam-marker/bank page: browse leaf questions across your papers, filter by
spec point (the spec-planning surface) and subject via facet chips, select
questions into a basket, and "Create paper" → POST /custom-papers → opens the new
template in setup. Dashboard gets a "Question bank" entry point.

examRepository.getBank + createCustomPaper; BankQuestion/BankResponse/custom-paper
types. tsc clean. Pairs with the mode-3 API endpoints (already merged).

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

src/types/exam.types.ts

@@ -338,3 +338,36 @@ export interface MarkUpsertPayload {
   comment?: string;
   confirmed?: boolean;
 }
+
+// ── Mode-3 question bank + custom-paper assembly ──────────────────────────────
+export interface BankQuestion {
+  id: string;
+  template_id: string;
+  label: string | null;
+  max_marks: number | null;
+  answer_type: string | null;
+  spec_ref: string | null;
+  bounds: Record<string, number> | null;
+  page: number | null;
+  paper: { id: string | null; title: string | null; subject: string | null; exam_code: string | null };
+}
+
+export interface BankResponse {
+  questions: BankQuestion[];
+  n: number;
+  facets: { spec_ref: Record<string, number>; subject: Record<string, number> };
+}
+
+export interface CreateCustomPaperPayload {
+  title: string;
+  subject?: string;
+  question_ids: string[];
+}
+
+export interface CreateCustomPaperResult {
+  id: string;
+  title: string;
+  subject: string | null;
+  n_questions: number;
+  n_response_areas: number;
+}