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.

Dockerfile

@@ -20,11 +20,10 @@ RUN apt-get update && apt-get install -y --no-install-recommends gosu \
 COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
 COPY --from=builder /usr/local/bin /usr/local/bin
 
-# Application code
-COPY config.py main.py alembic.ini entrypoint.sh ./
-COPY db/ ./db/
-COPY api/ ./api/
-COPY handlers/ ./handlers/
+# Application code (duty_teller package + entrypoint, migrations, webapp)
+ENV PYTHONPATH=/app
+COPY main.py alembic.ini entrypoint.sh ./
+COPY duty_teller/ ./duty_teller/
 COPY alembic/ ./alembic/
 COPY webapp/ ./webapp/