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.test.mjs

@@ -0,0 +1,80 @@
+// Tests for the public-link gate. Unit tests use synthetic content; the last test is the
+// FERDIG criterion and reads this repository's own README and manifest.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { spawnSync } from 'node:child_process';
+import { mkdirSync, mkdtempSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { PUBLIC_REPOS, extractRepoLinks, scanFiles, runCheck } from './check-public-links.mjs';
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+const REPO = join(HERE, '..');
+const CLI = join(HERE, 'check-public-links.mjs');
+
+test('extractRepoLinks finds every org-repo link with its line, dropping .git', () => {
+  const content = [
+    '# title',
+    '[a](https://git.fromaitochitta.com/open/voyage) and [b](https://git.fromaitochitta.com/open/okr/src/branch/main)',
+    '"url": "https://git.fromaitochitta.com/open/repo-mailbox.git"',
+    'https://example.com/open/not-ours',
+  ].join('\n');
+  assert.deepEqual(extractRepoLinks(content), [
+    { line: 2, repo: 'voyage' },
+    { line: 2, repo: 'okr' },
+    { line: 3, repo: 'repo-mailbox' },
+  ]);
+});
+
+test('scanFiles flags only links to repositories off the public list', () => {
+  const { links, findings } = scanFiles(
+    [
+      { path: 'README.md', content: 'https://git.fromaitochitta.com/open/voyage\nhttps://git.fromaitochitta.com/open/gone-private' },
+      { path: 'm.json', content: '"https://git.fromaitochitta.com/open/gone-private.git"' },
+    ],
+    ['voyage'],
+  );
+  assert.equal(links.length, 3);
+  assert.deepEqual(findings.map((f) => `${f.path}:${f.line}:${f.repo}`), ['README.md:2:gone-private', 'm.json:1:gone-private']);
+});
+
+test('the public list is sorted and has no duplicates', () => {
+  assert.deepEqual([...PUBLIC_REPOS].sort(), PUBLIC_REPOS);
+  assert.equal(new Set(PUBLIC_REPOS).size, PUBLIC_REPOS.length);
+});
+
+function tmpRoot(files) {
+  const root = mkdtempSync(join(tmpdir(), 'public-links-'));
+  for (const [path, body] of Object.entries(files)) {
+    mkdirSync(dirname(join(root, path)), { recursive: true });
+    writeFileSync(join(root, path), body);
+  }
+  return root;
+}
+
+test('CLI exits 1 on a hit and 0 on a clean surface, always printing the denominator', () => {
+  const run = (root) => spawnSync(process.execPath, [CLI, root], { encoding: 'utf8' });
+  const dirty = run(tmpRoot({ 'README.md': 'https://git.fromaitochitta.com/open/voyage\nhttps://git.fromaitochitta.com/open/gone-private\n' }));
+  assert.equal(dirty.status, 1);
+  assert.match(dirty.stdout, /\[ERROR\] link to a repository not listed as public — README\.md:2: open\/gone-private/);
+  assert.match(dirty.stdout, /2 org-repo links in 1\/2 files/);
+  const clean = run(tmpRoot({ '.claude-plugin/marketplace.json': '"https://git.fromaitochitta.com/open/voyage.git"' }));
+  assert.equal(clean.status, 0);
+  assert.match(clean.stdout, /1 org-repo links in 1\/2 files, \d+ public repos listed — 0 hit/);
+});
+
+test('CLI fails when it finds no links at all: verified nothing', () => {
+  const r = spawnSync(process.execPath, [CLI, tmpRoot({ 'README.md': 'no links\n' })], { encoding: 'utf8' });
+  assert.equal(r.status, 1);
+  assert.match(r.stdout, /verified nothing/);
+});
+
+// The FERDIG criterion: the catalog links only to repositories listed as public, and every
+// plugin in the manifest is one of them.
+test('this repository: README and manifest link only to public repositories', () => {
+  const { files, links, findings } = runCheck(REPO);
+  assert.equal(files, 2, 'both surface files present');
+  assert.ok(links.length > 0, '0 links found — verified nothing');
+  assert.deepEqual(findings.map((f) => `${f.path}:${f.line}: open/${f.repo}`), []);
+});