refactor: rewrite client as thin async HTTP layer and migrate all tools

Merged arturo requested to merge feature/overhaul into master
  • Replace domain-specific client methods with generic get/post/patch/put/delete
  • Introduce AudiobookshelfError with status_code, message, and body attributes
  • Tools call client HTTP verbs directly with API paths and JSON bodies
  • Rewrite test suite: 29 tests covering HTTP layer, auth injection, error handling, lifecycle, response shapes, and server integration
  • Add pytest-asyncio and respx to dev dependencies
  • Update requires-python to >=3.13, ruff target-version to py313
  • Rename token parameter to api_key in server entry point

Merge request reports