feat(qmd): add shared Node helpers and index.yml model block editing

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

shared/qmd/qmd-config.mjs

@@ -0,0 +1,34 @@
+// shared/qmd/qmd-config.mjs — edits only the models: block of QMD's index.yml.
+import { existsSync, readFileSync, writeFileSync, mkdirSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { pathToFileURL } from 'node:url';
+import { MODELS, qmdConfigPath, qmdPackageDir } from './qmd-lib.mjs';
+
+export function setModels(text, YAML) {
+  const document = YAML.parseDocument(text || '');
+  if (document.errors.length) throw new Error(`index.yml cannot be parsed: ${document.errors[0].message}`);
+  if (document.contents === null) document.contents = document.createNode({});
+  document.set('models', document.createNode({ ...MODELS }));
+  return document.toString();
+}
+
+export function unsetModels(text, YAML) {
+  const document = YAML.parseDocument(text || '');
+  if (document.errors.length) throw new Error(`index.yml cannot be parsed: ${document.errors[0].message}`);
+  if (document.contents !== null) document.delete('models');
+  return document.contents === null || document.contents.items?.length === 0 ? '' : document.toString();
+}
+
+async function main(action) {
+  if (!['set-models', 'unset-models'].includes(action)) throw new Error('usage: qmd-config.mjs set-models|unset-models');
+  const YAML = await import(pathToFileURL(join(qmdPackageDir(), 'node_modules', 'yaml', 'dist', 'index.js')).href);
+  const path = qmdConfigPath();
+  const current = existsSync(path) ? readFileSync(path, 'utf8') : '';
+  const next = action === 'set-models' ? setModels(current, YAML) : unsetModels(current, YAML);
+  mkdirSync(dirname(path), { recursive: true });
+  writeFileSync(path, next);
+}
+
+if (import.meta.url === pathToFileURL(process.argv[1] || '').href) {
+  main(process.argv[2]).catch((error) => { console.error(`qmd-config: ${error.message}`); process.exit(1); });
+}