docs(readme): promote native claude plugin commands as the recommended install path
Restructure README.md so the claude plugin marketplace add /
install / update / uninstall / marketplace remove commands
appear at the top as the recommended default. The native CLI path
only requires Claude Code (no Git), so it has a lower barrier to
entry for most users.
The irm / curl script-based installation is moved into an
"其他安裝方式：使用腳本" subsection further down, alongside its
prerequisites (Git), env vars table, and developer mode — since
those features are only relevant when users opt into the scripts.
Net result: -22 lines, no duplicate command listings, all plugin
references use the qualified hncc@hncc form per CLAUDE.md.