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.

api/app.py

@@ -0,0 +1,47 @@
+"""FastAPI app: /api/duties and static webapp."""
+from pathlib import Path
+
+import config
+from fastapi import FastAPI, Query
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.staticfiles import StaticFiles
+
+from db.session import get_session
+from db.repository import get_duties
+from db.schemas import DutyWithUser
+
+app = FastAPI(title="Duty Teller API")
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+@app.get("/api/duties", response_model=list[DutyWithUser])
+def list_duties(
+    from_date: str = Query(..., description="ISO date YYYY-MM-DD"),
+    to_date: str = Query(..., description="ISO date YYYY-MM-DD"),
+) -> list[DutyWithUser]:
+    session = get_session(config.DATABASE_URL)
+    try:
+        rows = get_duties(session, from_date=from_date, to_date=to_date)
+        return [
+            DutyWithUser(
+                id=duty.id,
+                user_id=duty.user_id,
+                start_at=duty.start_at,
+                end_at=duty.end_at,
+                full_name=full_name,
+            )
+            for duty, full_name in rows
+        ]
+    finally:
+        session.close()
+
+
+webapp_path = Path(__file__).resolve().parent.parent / "webapp"
+if webapp_path.is_dir():
+    app.mount("/app", StaticFiles(directory=str(webapp_path), html=True), name="webapp")