fix(web): vocab form-level error states, newVocabulary heading, id guard, EN-required test

web/src/vocab/vocabulary-list.tsx

@@ -27,6 +27,7 @@ export function VocabularyList() {
   return (
     <div className="flex h-full flex-col">
       <form onSubmit={onCreate} className="space-y-1 border-b p-3">
+        <div className="text-sm font-medium">{t("vocab.newVocabulary")}</div>
         <Label htmlFor="vocab-key">{t("vocab.key")}</Label>
         <div className="flex gap-2">
           <Input
@@ -38,6 +39,11 @@ export function VocabularyList() {
             {t("vocab.create")}
           </Button>
         </div>
+        {create.isError && (
+          <p role="alert" className="text-xs text-red-600">
+            {t("form.rejected")}
+          </p>
+        )}
       </form>
       <ul className="flex-1 overflow-auto">
         {isLoading && (