feat: Sprint 2 — test taking + results

Backend:
- Models: TestAttempt, AttemptAnswer (migration 002)
- POST /api/attempts: start attempt, shuffle questions/answers,
  hide is_correct, expose is_multiple for UI hints
- POST /api/attempts/{id}/submit: save answers, calculate score,
  strict matching (selected == correct), return full result
- GET /api/attempts/{id}/result: fetch saved result
- Register attempts router in main.py

Frontend:
- api/attempts.ts: types + API functions
- TestTake page: one question at a time, progress bar, timer
  with auto-submit, back navigation controlled by test setting,
  radio/checkbox based on is_multiple
- AttemptResult page: score, pass/fail, per-question breakdown
  with correct/selected/missed answer highlighting
- App.tsx: add /tests/:testId/take and /attempts/:id/result routes
- TestDetail: add "Пройти тест" button

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/TestDetail/index.tsx

@@ -1,4 +1,4 @@
-import { ArrowLeftOutlined, CheckCircleTwoTone, CloseCircleTwoTone } from '@ant-design/icons'
+import { ArrowLeftOutlined, CheckCircleTwoTone, CloseCircleTwoTone, PlayCircleOutlined } from '@ant-design/icons'
 import { useQuery } from '@tanstack/react-query'
 import { Button, Card, Descriptions, List, Space, Spin, Tag, Typography } from 'antd'
 import { useNavigate, useParams } from 'react-router-dom'
@@ -24,10 +24,17 @@ export default function TestDetail() {
 
   return (
     <div style={{ maxWidth: 820, margin: '0 auto', padding: 24 }}>
-      <Space style={{ marginBottom: 16 }}>
+      <Space style={{ width: '100%', justifyContent: 'space-between', marginBottom: 16 }}>
         <Button icon={<ArrowLeftOutlined />} onClick={() => navigate('/')}>
           К списку тестов
         </Button>
+        <Button
+          type="primary"
+          icon={<PlayCircleOutlined />}
+          onClick={() => navigate(`/tests/${test.id}/take`)}
+        >
+          Пройти тест
+        </Button>
       </Space>
 
       <Title level={2}>{test.title}</Title>