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>

backend/alembic/versions/002_attempts.py

@@ -0,0 +1,53 @@
+"""attempts
+
+Revision ID: 002
+Revises: 001
+Create Date: 2026-03-21
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "002"
+down_revision: Union[str, None] = "001"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "test_attempts",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("test_id", sa.Integer(), sa.ForeignKey("tests.id"), nullable=False),
+        sa.Column(
+            "started_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("now()"),
+            nullable=False,
+        ),
+        sa.Column("finished_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("score", sa.Float(), nullable=True),
+        sa.Column("passed", sa.Boolean(), nullable=True),
+        sa.Column("correct_count", sa.Integer(), nullable=True),
+        sa.Column("total_count", sa.Integer(), nullable=True),
+        sa.Column("status", sa.String(20), nullable=False, server_default="in_progress"),
+        sa.PrimaryKeyConstraint("id"),
+    )
+
+    op.create_table(
+        "attempt_answers",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column(
+            "attempt_id", sa.Integer(), sa.ForeignKey("test_attempts.id"), nullable=False
+        ),
+        sa.Column("question_id", sa.Integer(), sa.ForeignKey("questions.id"), nullable=False),
+        sa.Column("answer_id", sa.Integer(), sa.ForeignKey("answers.id"), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("attempt_answers")
+    op.drop_table("test_attempts")