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/schemas.py

@@ -0,0 +1,43 @@
+"""Pydantic schemas for API and validation."""
+from pydantic import BaseModel, ConfigDict
+
+
+class UserBase(BaseModel):
+    full_name: str
+    username: str | None = None
+    first_name: str | None = None
+    last_name: str | None = None
+
+
+class UserCreate(UserBase):
+    telegram_user_id: int
+
+
+class UserInDb(UserBase):
+    id: int
+    telegram_user_id: int
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class DutyBase(BaseModel):
+    user_id: int
+    start_at: str  # ISO 8601
+    end_at: str    # ISO 8601
+
+
+class DutyCreate(DutyBase):
+    pass
+
+
+class DutyInDb(DutyBase):
+    id: int
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class DutyWithUser(DutyInDb):
+    """Duty with full_name for calendar display."""
+    full_name: str
+
+    model_config = ConfigDict(from_attributes=True)