Enhance database initialization and improve command handling

- Added `__all__` declaration in `db/__init__.py` for better module export management.
- Simplified command text formatting in `handlers/commands.py` for improved readability.
- Refactored error handler function signature in `handlers/errors.py` for better code style.
- Introduced comprehensive tests for API duties and Telegram authentication in new test files.

db/__init__.py

@@ -5,6 +5,24 @@ from db.schemas import UserCreate, UserInDb, DutyCreate, DutyInDb, DutyWithUser
 from db.session import get_engine, get_session_factory, get_session
 from db.repository import get_or_create_user, get_duties, insert_duty
 
+__all__ = [
+    "Base",
+    "User",
+    "Duty",
+    "UserCreate",
+    "UserInDb",
+    "DutyCreate",
+    "DutyInDb",
+    "DutyWithUser",
+    "get_engine",
+    "get_session_factory",
+    "get_session",
+    "get_or_create_user",
+    "get_duties",
+    "insert_duty",
+    "init_db",
+]
+
 
 def init_db(database_url: str) -> None:
     """Create tables from metadata (Alembic migrations handle schema in production)."""