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/tasks.py

@@ -10,7 +10,7 @@ from services.user_service import UserService
 from services.task_service import TaskService
 from services.vocabulary_service import VocabularyService
 from services.ai_service import ai_service
-from utils.i18n import t, get_user_lang
+from utils.i18n import t, get_user_lang, get_user_translation_lang
 from utils.levels import get_user_level_for_language
 
 router = Router()
@@ -69,7 +69,7 @@ async def start_vocabulary_tasks(callback: CallbackQuery, state: FSMContext):
         tasks = await TaskService.generate_mixed_tasks(
             session, user.id, count=5,
             learning_lang=user.learning_language,
-            translation_lang=user.language_interface,
+            translation_lang=get_user_translation_lang(user),
         )
 
         if not tasks:
@@ -122,12 +122,13 @@ async def start_new_words_tasks(callback: CallbackQuery, state: FSMContext):
         exclude_words = list(set(vocab_words + correct_task_words))
 
         # Генерируем новые слова через AI
+        translation_lang = get_user_translation_lang(user)
         words = await ai_service.generate_thematic_words(
             theme="random everyday vocabulary",
             level=level,
             count=5,
             learning_lang=user.learning_language,
-            translation_lang=user.language_interface,
+            translation_lang=translation_lang,
             exclude_words=exclude_words if exclude_words else None,
         )
 
@@ -138,7 +139,7 @@ async def start_new_words_tasks(callback: CallbackQuery, state: FSMContext):
 
         # Преобразуем слова в задания
         tasks = []
-        translate_prompt = t(lang, 'tasks.translate_to', lang_name=t(lang, f'lang.{user.language_interface}'))
+        translate_prompt = t(lang, 'tasks.translate_to', lang_name=t(lang, f'lang.{translation_lang}'))
         for word in words:
             tasks.append({
                 'type': 'translate',
@@ -168,6 +169,7 @@ async def show_current_task(message: Message, state: FSMContext):
     data = await state.get_data()
     tasks = data.get('tasks', [])
     current_index = data.get('current_task_index', 0)
+    user_id = data.get('user_id')
 
     if current_index >= len(tasks):
         # Все задания выполнены
@@ -176,9 +178,9 @@ async def show_current_task(message: Message, state: FSMContext):
 
     task = tasks[current_index]
 
-    # Определяем язык пользователя
+    # Определяем язык пользователя (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'
 
     task_text = (
@@ -349,7 +351,7 @@ async def add_task_word(callback: CallbackQuery, state: FSMContext):
             word_original=word,
             word_translation=translation,
             source_lang=user.learning_language,
-            translation_lang=user.language_interface,
+            translation_lang=get_user_translation_lang(user),
             transcription=transcription,
             source=WordSource.AI_TASK
         )
@@ -409,6 +411,7 @@ async def finish_tasks(message: Message, state: FSMContext):
     tasks = data.get('tasks', [])
     correct_count = data.get('correct_count', 0)
     total_count = len(tasks)
+    user_id = data.get('user_id')
 
     accuracy = int((correct_count / total_count) * 100) if total_count > 0 else 0
 
@@ -426,9 +429,9 @@ async def finish_tasks(message: Message, state: FSMContext):
         emoji = "💪"
         comment_key = 'poor'
 
-    # Язык пользователя
+    # Язык пользователя (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'
 
     result_text = (