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.

pyproject.toml

@@ -0,0 +1,38 @@
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "duty-teller"
+version = "0.1.0"
+description = "Telegram bot for team duty shift calendar and group reminder"
+readme = "README.md"
+requires-python = ">=3.11"
+dependencies = [
+    "python-telegram-bot[job-queue]>=22.0,<23.0",
+    "python-dotenv>=1.0,<2.0",
+    "fastapi>=0.115,<1.0",
+    "uvicorn[standard]>=0.32,<1.0",
+    "sqlalchemy>=2.0,<3.0",
+    "alembic>=1.14,<2.0",
+    "pydantic>=2.0,<3.0",
+    "icalendar>=5.0,<6.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0,<9.0",
+    "pytest-asyncio>=0.24,<1.0",
+    "httpx>=0.27,<1.0",
+]
+
+[tool.setuptools.packages.find]
+where = ["."]
+include = ["db", "handlers", "api", "importers", "utils", "services"]
+
+[tool.black]
+line-length = 120
+target-version = ["py311"]
+
+[tool.pylint.messages_control]
+disable = ["C0114", "C0115", "C0116"]