Enhance API and configuration for Telegram miniapp

- Added support for CORS origins and a new environment variable for miniapp access control.
- Implemented date validation for API requests to ensure correct date formats.
- Updated FastAPI app to allow access without Telegram initData for local development.
- Enhanced error handling and logging for better debugging.
- Added tests for API functionality and Telegram initData validation.
- Updated README with new environment variable details and testing instructions.
- Modified Docker and Git ignore files to include additional directories and files.

db/session.py

@@ -1,4 +1,7 @@
 """SQLAlchemy engine and session factory."""
+from contextlib import contextmanager
+from typing import Generator
+
 from sqlalchemy import create_engine
 from sqlalchemy.orm import Session, sessionmaker
 
@@ -8,6 +11,16 @@ _engine = None
 _SessionLocal = None
 
 
+@contextmanager
+def session_scope(database_url: str) -> Generator[Session, None, None]:
+    """Context manager: yields a session and closes it on exit."""
+    session = get_session(database_url)
+    try:
+        yield session
+    finally:
+        session.close()
+
+
 def get_engine(database_url: str):
     global _engine
     if _engine is None: