Simplify community Plugin contributions

[hetaoBackend]

What changed

• Replace the external-repository registry flow with directly hosted plugins/<owner>/<plugin> packages.
• Add npm run create -- <owner>/<plugin> and repository-level hosted Plugin validation.
• Remove registry JSON, commit pinning, remote verification scripts, and the redundant submission workflow.
• Redesign the English and Chinese README around a one-folder, one-PR contribution path, with a new repository-owned hero.
• Update contribution, architecture, compatibility, governance, and security documentation.

Why

The first version asked contributors to maintain a separate repository and submit a pinned catalog record. That was too much ceremony for a community repository whose immediate job is to accept useful Plugins.

The new path makes the reviewed source the published source. Contributors create one directory, run one check, and open one pull request.

User impact

npm run create -- <github-owner>/<plugin-name>
npm run check

The scaffold produces a Skill-first package with plugin.json, README.md, LICENSE, and SKILL.md. CI rejects unfinished templates, invalid package contracts, unsafe paths, and symlinks.

Validation

• npm ci
• npm run check — 12 tests passed
• git diff --check
• local Markdown link verification
• 1200×360 README hero rendered and visually inspected