Refactor project structure and enhance Docker configuration

- Updated `.dockerignore` to exclude test and development artifacts, optimizing the Docker image size.
- Refactored `main.py` to delegate execution to `duty_teller.run.main()`, simplifying the entry point.
- Introduced a new `duty_teller` package to encapsulate core functionality, improving modularity and organization.
- Enhanced `pyproject.toml` to define a script for running the application, streamlining the execution process.
- Updated README documentation to reflect changes in project structure and usage instructions.
- Improved Alembic environment configuration to utilize the new package structure for database migrations.

duty_teller/__init__.py

@@ -0,0 +1,8 @@
+"""Duty Teller: Telegram bot for team duty shift calendar and group reminder."""
+
+from importlib.metadata import version, PackageNotFoundError
+
+try:
+    __version__ = version("duty-teller")
+except PackageNotFoundError:
+    __version__ = "0.1.0"