refactor(clients): reorganize client modules into clients package

- Move auth, user, and music clients into new clients package
- Update imports to use new module paths
- Add __init__.py to expose clients from package
- Clean up code formatting and imports
- Add pre-commit configuration for code quality checks

.gitignore

@@ -170,4 +170,4 @@ cython_debug/
 
 venv/*
 Documents.md
-test.py
+test.py