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.

conftest.py

@@ -1,7 +1,6 @@
-"""Pytest configuration. Set BOT_TOKEN so config module can be imported."""
+"""Pytest configuration. BOT_TOKEN no longer required at import; set for tests that need it."""
 
 import os
 
-# Set before any project code imports config (which requires BOT_TOKEN).
 if not os.environ.get("BOT_TOKEN"):
     os.environ["BOT_TOKEN"] = "test-token-for-pytest"