website: gate every yaml config example against the real plugin surface

New doc-sync gate verify-website-yaml: each ```yaml block under
website/zh-CN (api/ excluded — generator-owned) must parse with the loader's
real schema (JSON_SCHEMA + !!js), use only EntryOptions keys, name only real
workspace packages, and pass only config keys the plugin's declared Config
type / schemastery schema accepts (collectConfigCatalog drives the key sets).
```yaml ignore-check opts out a deliberate-placeholder block (the
capability-trio tutorial keeps its fictional package names).

scripts/run-gates.ts

@@ -274,6 +274,7 @@ function docSyncLeafGates(): Gate[] {
     pnpmScript('type-equivalence', 'verify-type-equiv', { label: 'type equivalence' }),
     pnpmScript('translation-pairing', 'verify-translation-pairing', { label: 'translation pairing' }),
     pnpmScript('doc-budgets', 'verify-doc-budgets', { label: 'doc budgets' }),
+    pnpmScript('website-yaml', 'verify-website-yaml', { label: 'website yaml' }),
   ]
 }