Enhance Telegram bot with database integration and API features

- Added SQLite database support with Alembic for migrations.
- Implemented FastAPI for HTTP API to manage duties.
- Updated configuration to include database URL and HTTP port.
- Created entrypoint script for Docker to handle migrations and permissions.
- Expanded command handlers to register users and display duties.
- Developed a web application for calendar display of duties.
- Included necessary Pydantic schemas and SQLAlchemy models for data handling.
- Updated requirements.txt to include new dependencies for FastAPI and SQLAlchemy.

db/session.py

@@ -0,0 +1,31 @@
+"""SQLAlchemy engine and session factory."""
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session, sessionmaker
+
+from db.models import Base
+
+_engine = None
+_SessionLocal = None
+
+
+def get_engine(database_url: str):
+    global _engine
+    if _engine is None:
+        _engine = create_engine(
+            database_url,
+            connect_args={"check_same_thread": False} if "sqlite" in database_url else {},
+            echo=False,
+        )
+    return _engine
+
+
+def get_session_factory(database_url: str) -> sessionmaker[Session]:
+    global _SessionLocal
+    if _SessionLocal is None:
+        engine = get_engine(database_url)
+        _SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+    return _SessionLocal
+
+
+def get_session(database_url: str) -> Session:
+    return get_session_factory(database_url)()