feat: add version history section to test edit page

- GET /api/tests/{id}/versions — returns full version chain from oldest to newest
- TestEdit: shows 'История версий' table when multiple versions exist,
  current version highlighted, links to navigate between versions

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

backend/app/api/tests.py

@@ -80,6 +80,44 @@ async def create_test(data: TestCreate, db: AsyncSession = Depends(get_db)):
     return result.scalar_one()
 
 
+@router.get("/{test_id}/versions", response_model=list[TestListItem])
+async def get_test_versions(test_id: int, db: AsyncSession = Depends(get_db)):
+    """Возвращает все версии теста (от первой к последней)."""
+    # Загружаем текущий тест
+    result = await db.execute(select(Test).where(Test.id == test_id))
+    test = result.scalar_one_or_none()
+    if not test:
+        raise HTTPException(status_code=404, detail="Тест не найден")
+
+    # Идём вверх до корневой версии
+    root = test
+    while root.parent_id is not None:
+        result = await db.execute(select(Test).where(Test.id == root.parent_id))
+        root = result.scalar_one()
+
+    # Идём вниз от корня, собирая цепочку
+    versions: list[Test] = []
+    current = root
+    while current is not None:
+        result = await db.execute(
+            select(Test)
+            .options(selectinload(Test.questions))
+            .where(Test.id == current.id)
+        )
+        current_with_qs = result.scalar_one()
+        versions.append(current_with_qs)
+
+        result = await db.execute(select(Test).where(Test.parent_id == current.id))
+        current = result.scalar_one_or_none()
+
+    items = []
+    for v in versions:
+        item = TestListItem.model_validate(v)
+        item.questions_count = len(v.questions)
+        items.append(item)
+    return items
+
+
 @router.put("/{test_id}", response_model=TestUpdateResponse)
 async def update_test(test_id: int, data: TestCreate, db: AsyncSession = Depends(get_db)):
     result = await db.execute(