chore(catalog): remove plugins that are no longer published

Remove claude-design from the marketplace manifest and its catalog
README entry, and remove the playground-design-system entry from the
README. The catalog now lists 11 plugins.

Add scripts/check-public-links.mjs: fails when README.md or the
manifest links to an open/<name> repository missing from a tracked
PUBLIC_REPOS list. Chosen over the local retired-terms list because
that gate scans every tracked file, and historical docs plus
CONVENTIONS.md (which keep naming these repos on purpose) would hold
it red; a live visibility check could not be red before the repos
change visibility. Red on 5ba4a7a (6 hits), green after (0 of 36).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/check-public-links.mjs

@@ -0,0 +1,85 @@
+#!/usr/bin/env node
+// Public-link gate: fails when the catalog's public surface (README.md, the marketplace
+// manifest) links to an org repository that is not on the tracked list of public repos
+// below. A repository that is made private or removed turns every link to it into a dead
+// link — and a manifest entry into a broken install — so the catalog may only point at
+// repositories that are deliberately listed as public here.
+//
+// Usage: node scripts/check-public-links.mjs [repo-root]
+//   exit 0 = checked, 0 hits · exit 1 = hit(s), or 0 links found (verified nothing)
+//
+// Adding a plugin to the catalog means adding its repository to PUBLIC_REPOS in the same
+// commit; removing one means taking it out of both.
+import { existsSync, readFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+
+// Org repositories the catalog may link to — the published plugins plus this catalog.
+export const PUBLIC_REPOS = [
+  'ai-psychosis',
+  'config-audit',
+  'graceful-handoff',
+  'human-friendly-style',
+  'ktg-plugin-marketplace',
+  'linkedin-studio',
+  'llm-security',
+  'ms-ai-architect',
+  'okr',
+  'repo-mailbox',
+  'repo-standard',
+  'voyage',
+];
+
+// The files a reader or an installer reaches from the catalog.
+export const SURFACE_FILES = ['README.md', '.claude-plugin/marketplace.json'];
+
+const LINK = /git\.fromaitochitta\.com\/open\/([A-Za-z0-9._-]+)/g;
+
+// Returns one { line, repo } per org-repo link in `content`; a trailing `.git` is dropped.
+export function extractRepoLinks(content) {
+  const links = [];
+  content.split('\n').forEach((text, i) => {
+    for (const m of text.matchAll(LINK)) links.push({ line: i + 1, repo: m[1].replace(/\.git$/, '') });
+  });
+  return links;
+}
+
+// files: [{ path, content }]. Returns every link plus the ones not on the public list.
+export function scanFiles(files, publicRepos = PUBLIC_REPOS) {
+  const links = [];
+  for (const { path, content } of files) {
+    for (const l of extractRepoLinks(content)) links.push({ path, ...l });
+  }
+  return { links, findings: links.filter((l) => !publicRepos.includes(l.repo)) };
+}
+
+export function runCheck(root) {
+  const files = SURFACE_FILES.filter((p) => existsSync(join(root, p))).map((path) => ({
+    path,
+    content: readFileSync(join(root, path), 'utf8'),
+  }));
+  return { files: files.length, ...scanFiles(files) };
+}
+
+function main(argv) {
+  const root = argv[0] ?? join(HERE, '..');
+  const { files, links, findings } = runCheck(root);
+  for (const f of findings) {
+    console.log(`[ERROR] link to a repository not listed as public — ${f.path}:${f.line}: open/${f.repo}`);
+  }
+  console.log(
+    `check-public-links: ${links.length} org-repo links in ${files}/${SURFACE_FILES.length} files, ` +
+      `${PUBLIC_REPOS.length} public repos listed — ${findings.length} hit(s)`,
+  );
+  if (links.length === 0) {
+    console.log('check-public-links: 0 links found — verified nothing');
+    return 1;
+  }
+  return findings.length > 0 ? 1 : 0;
+}
+
+if (process.argv[1] && fileURLToPath(import.meta.url) === process.argv[1]) {
+  process.exit(main(process.argv.slice(2)));
+}