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.

tests/test_repository_duty_range.py

@@ -4,8 +4,8 @@ import pytest
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
-from db.models import Base, User
-from db.repository import (
+from duty_teller.db.models import Base, User
+from duty_teller.db.repository import (
     delete_duties_in_range,
     get_or_create_user_by_full_name,
     get_duties,