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_import_duty_schedule_integration.py

@@ -4,15 +4,15 @@ from datetime import date
 
 import pytest
 
-from db import init_db
-from db.repository import get_duties
-from db.session import get_session, session_scope
-from importers.duty_schedule import (
+from duty_teller.db import init_db
+from duty_teller.db.repository import get_duties
+from duty_teller.db.session import get_session, session_scope
+from duty_teller.importers.duty_schedule import (
     DutyScheduleEntry,
     DutyScheduleResult,
     parse_duty_schedule,
 )
-from services.import_service import run_import
+from duty_teller.services.import_service import run_import
 
 
 @pytest.fixture
@@ -23,7 +23,7 @@ def db_url():
 @pytest.fixture(autouse=True)
 def _reset_db_session(db_url):
     """Ensure each test uses a fresh engine for :memory: (clear global cache for test URL)."""
-    import db.session as session_module
+    import duty_teller.db.session as session_module
 
     session_module._engine = None
     session_module._SessionLocal = None