feat(quiz): variety in quiz question selection

Expand the seeded pool from 12 to 36 questions (migration 0020) and
select 10 per session preferring questions the couple has never seen,
then least recently used, with random tiebreaks, so repeat quizzes stop
serving the same set.

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

apps/api/src/domains/quiz/repository.ts

@@ -167,9 +167,22 @@ export class PostgresQuizRepository implements QuizRepository {
         return { session: await this.buildPayload(client, existing.rows[0], userId), created: false };
       }
 
+      // Prefer questions this couple has never had in any prior session (completed or
+      // active), then the least-recently-used ones, with a random tiebreak within each
+      // group so repeat quizzes stay varied instead of always reusing the same pool.
       const questions = await client.query<{ id: string }>(
-        'select id from quiz_questions where is_active = true order by sort_order, id limit $1',
-        [QUESTIONS_PER_SESSION],
+        `select q.id
+         from quiz_questions q
+         left join (
+           select question_id, max(created_at) as last_used
+           from quiz_sessions, unnest(question_ids) as question_id
+           where couple_id = $1
+           group by question_id
+         ) usage on usage.question_id = q.id
+         where q.is_active = true
+         order by (usage.last_used is not null), usage.last_used asc, random()
+         limit $2`,
+        [coupleId, QUESTIONS_PER_SESSION],
       );
       const questionIds = questions.rows.map((row) => row.id);