fix: enforce plugins/<site> registration in root webcmd-plugin.json

[ayushsingh82]

Summary

• Promoting a CLI to a repo plugin has an easy-to-skip step: after webcmd plugin create scaffolds plugins/<site>/, the author must also register <site> in the root webcmd-plugin.json plugins map. Nothing in webcmd plugin create, webcmd plugin install file://..., or webcmd validate <site> errors or warns when that registration is skipped — the plugin works locally either way. Per the issue, three separate adapter builds (manchester, warwick, mdxdubai) all missed it silently.
• Adds scripts/check-plugin-root-registration.mjs: fails when a plugins/<site> directory has no matching root-manifest entry, and also catches the reverse (a root-manifest entry with no matching directory). Mirrors the style/location of the existing scripts/check-plugin-command-parity.mjs.
• Adds check:plugin-root-registration to package.json.
• Adds a verification step to the adapter-template.md promotion sequence so an agent following the skill catches the gap immediately, not just at CI time.

Fixes #222

Not included: CI wiring

I'd normally add this as a step in .github/workflows/ci.yml right next to the existing "Check plugin command parity" step, but my fork's token doesn't have the workflow scope GitHub requires to push workflow-file changes. A maintainer can add:

      - name: Check plugin root registration
        if: runner.os == 'Linux'
        run: npm run check:plugin-root-registration

right after the check:plugin-parity step in the build job (.github/workflows/ci.yml) — happy to open a follow-up once I sort out the token scope, whichever is easier for you.

Test plan

• Verified the check fails when a plugins/<site> dir exists without a root-manifest entry (simulated with a throwaway fixture dir, removed after)
• Verified the check fails the other direction too (a root-manifest entry with no matching dir)
• Verified it passes clean against the current repo (123 plugins, all registered)
• npm run typecheck clean
• npm test — 385 test files / 4623 passed, 1 skipped (unchanged baseline)

[ayushsingh82]

@ngaurav Fixed — this PR adds scripts/check-plugin-root-registration.mjs (catches a plugins/ directory with no matching root webcmd-plugin.json entry, or vice versa) plus a verification step in the adapter-template.md promotion sequence, closing #222. CI wiring is noted in the PR description since my fork's token currently lacks the workflow scope to push that part myself.

[github-actions]

🟢 No documentation gap found — medium confidence

The automated review found no documentation gap in the supplied changes.

This review is advisory and does not block merging.