feat: add translation language setting & onboarding flow

- Add separate translation_language setting (independent from interface language)
- Implement 3-step onboarding for new users:
  1. Choose interface language
  2. Choose learning language
  3. Choose translation language
- Fix localization issues when using callback.message (user_id from state)
- Add UserService.get_user_by_id() method
- Add get_user_translation_lang() helper in i18n
- Update all handlers to use correct translation language
- Add localization keys for onboarding (ru/en/ja)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

bot/handlers/level_test.py

@@ -24,11 +24,14 @@ async def cmd_level_test(message: Message, state: FSMContext):
     await start_level_test(message, state)
 
 
-async def start_level_test(message: Message, state: FSMContext):
+async def start_level_test(message: Message, state: FSMContext, telegram_id: int = None):
     """Начать тест определения уровня"""
+    # Определяем ID пользователя (telegram_id передаётся при вызове из callback)
+    user_telegram_id = telegram_id or message.from_user.id
+
     # Показываем описание теста
     async with async_session_maker() as session:
-        user = await UserService.get_user_by_telegram_id(session, message.from_user.id)
+        user = await UserService.get_user_by_telegram_id(session, user_telegram_id)
     lang = (user.language_interface if user else 'ru') or 'ru'
     await message.answer(t(lang, 'level_test.intro'))
 
@@ -83,7 +86,8 @@ async def begin_test(callback: CallbackQuery, state: FSMContext):
         current_question=0,
         correct_answers=0,
         answers=[],  # Для отслеживания ответов по уровням
-        learning_language=learning_lang
+        learning_language=learning_lang,
+        user_id=user.id
     )
     await state.set_state(LevelTestStates.taking_test)
 
@@ -96,6 +100,7 @@ async def show_question(message: Message, state: FSMContext):
     data = await state.get_data()
     questions = data.get('questions', [])
     current_idx = data.get('current_question', 0)
+    user_id = data.get('user_id')
 
     if current_idx >= len(questions):
         # Тест завершён
@@ -105,9 +110,9 @@ async def show_question(message: Message, state: FSMContext):
     question = questions[current_idx]
 
     # Формируем текст вопроса
-    # Язык интерфейса
+    # Язык интерфейса (берём user_id из state, т.к. message может быть от бота)
     async with async_session_maker() as session:
-        user = await UserService.get_user_by_telegram_id(session, message.from_user.id)
+        user = await UserService.get_user_by_id(session, user_id)
     lang = (user.language_interface if user else 'ru') or 'ru'
 
     text = (
@@ -127,10 +132,6 @@ async def show_question(message: Message, state: FSMContext):
         ])
 
     # Кнопка для показа перевода вопроса (локализованная)
-    async with async_session_maker() as session:
-        user = await UserService.get_user_by_telegram_id(session, message.chat.id)
-    from utils.i18n import t
-    lang = (user.language_interface if user else 'ru') or 'ru'
     keyboard.append([
         InlineKeyboardButton(text=t(lang, 'level_test.show_translation_btn'), callback_data=f"show_qtr_{current_idx}")
     ])
@@ -237,6 +238,7 @@ async def finish_test(message: Message, state: FSMContext):
     correct_answers = data.get('correct_answers', 0)
     answers = data.get('answers', [])
     learning_lang = data.get('learning_language', 'en')
+    user_id = data.get('user_id')
 
     total = len(questions)
     accuracy = int((correct_answers / total) * 100) if total > 0 else 0
@@ -244,9 +246,9 @@ async def finish_test(message: Message, state: FSMContext):
     # Определяем уровень на основе правильных ответов по уровням
     level = determine_level(answers, learning_lang)
 
-    # Сохраняем уровень в базе данных
+    # Сохраняем уровень в базе данных (берём user_id из state, т.к. message может быть от бота)
     async with async_session_maker() as session:
-        user = await UserService.get_user_by_telegram_id(session, message.chat.id)
+        user = await UserService.get_user_by_id(session, user_id)
         if user:
             await UserService.update_user_level(session, user.id, level, learning_lang)