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_utils.py

@@ -4,15 +4,15 @@ from datetime import date
 
 import pytest
 
-from utils.dates import (
+from duty_teller.utils.dates import (
     day_start_iso,
     day_end_iso,
     duty_to_iso,
     parse_iso_date,
     validate_date_range,
 )
-from utils.user import build_full_name
-from utils.handover import parse_handover_time
+from duty_teller.utils.user import build_full_name
+from duty_teller.utils.handover import parse_handover_time
 
 
 # --- dates ---