Remove legacy engine and many plugin modules, refactor upload plugins to standalone classes, and simplify package entry points. __init__.py now provides a safe __version__ fallback; __main__.py directly invokes stream_gears.main_loop. BiliWeb/BiliWebAsync plugins were adapted to use a FileInfo NamedTuple and no longer depend on engine.UploadBase/Plugin decorator. Documentation updated (README expanded with new commands and CLI/SKILL integration) and a new SKILL.md added. Workspace version bumped to 1.2.1 in Cargo.toml (lock updated accordingly).