Add configuration rules, refactor settings management, and enhance import functionality

- Introduced a new configuration file `.cursorrules` to define coding standards, error handling, testing requirements, and project-specific guidelines.
- Refactored `config.py` to implement a `Settings` dataclass for better management of environment variables, improving testability and maintainability.
- Updated the import duty schedule handler to utilize session management with `session_scope`, ensuring proper database session handling.
- Enhanced the import service to streamline the duty schedule import process, improving code organization and readability.
- Added new service layer functions to encapsulate business logic related to group duty pinning and duty schedule imports.
- Updated README documentation to reflect the new configuration structure and improved import functionality.

tests/test_repository_duty_range.py

@@ -4,7 +4,7 @@ import pytest
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
-from db.models import Base, User, Duty
+from db.models import Base, User
 from db.repository import (
     delete_duties_in_range,
     get_or_create_user_by_full_name,
@@ -15,7 +15,9 @@ from db.repository import (
 
 @pytest.fixture
 def session():
-    engine = create_engine("sqlite:///:memory:", connect_args={"check_same_thread": False})
+    engine = create_engine(
+        "sqlite:///:memory:", connect_args={"check_same_thread": False}
+    )
     Base.metadata.create_all(engine)
     Session = sessionmaker(bind=engine, autocommit=False, autoflush=False)
     s = Session()