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/repository.py

@@ -0,0 +1,61 @@
+"""Repository: get_or_create_user, get_duties, insert_duty."""
+from sqlalchemy.orm import Session
+
+from db.models import User, Duty
+
+
+def get_or_create_user(
+    session: Session,
+    telegram_user_id: int,
+    full_name: str,
+    username: str | None = None,
+    first_name: str | None = None,
+    last_name: str | None = None,
+) -> User:
+    user = session.query(User).filter(User.telegram_user_id == telegram_user_id).first()
+    if user:
+        user.full_name = full_name
+        user.username = username
+        user.first_name = first_name
+        user.last_name = last_name
+        session.commit()
+        session.refresh(user)
+        return user
+    user = User(
+        telegram_user_id=telegram_user_id,
+        full_name=full_name,
+        username=username,
+        first_name=first_name,
+        last_name=last_name,
+    )
+    session.add(user)
+    session.commit()
+    session.refresh(user)
+    return user
+
+
+def get_duties(
+    session: Session,
+    from_date: str,
+    to_date: str,
+) -> list[tuple[Duty, str]]:
+    """Return list of (Duty, full_name) overlapping the given date range (ISO date strings)."""
+    q = (
+        session.query(Duty, User.full_name)
+        .join(User, Duty.user_id == User.id)
+        .filter(Duty.start_at <= to_date, Duty.end_at >= from_date)
+    )
+    return list(q.all())
+
+
+def insert_duty(
+    session: Session,
+    user_id: int,
+    start_at: str,
+    end_at: str,
+) -> Duty:
+    duty = Duty(user_id=user_id, start_at=start_at, end_at=end_at)
+    session.add(duty)
+    session.commit()
+    session.refresh(duty)
+    return duty