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.

duty_teller/services/__init__.py

@@ -0,0 +1,23 @@
+"""Service layer: business logic and orchestration."""
+
+from duty_teller.services.group_duty_pin_service import (
+    format_duty_message,
+    get_duty_message_text,
+    get_next_shift_end_utc,
+    save_pin,
+    delete_pin,
+    get_message_id,
+    get_all_pin_chat_ids,
+)
+from duty_teller.services.import_service import run_import
+
+__all__ = [
+    "format_duty_message",
+    "get_duty_message_text",
+    "get_next_shift_end_utc",
+    "save_pin",
+    "delete_pin",
+    "get_message_id",
+    "get_all_pin_chat_ids",
+    "run_import",
+]