fix(frontend): harden the streaming ui and extract copy and constants

frontend/src/components/StreamError.vue

@@ -1,4 +1,6 @@
 <script setup lang="ts">
+import { messages } from '../lib/messages'
+
 defineProps<{ code: string; message: string }>()
 defineEmits<{ retry: [] }>()
 </script>
@@ -6,7 +8,7 @@ defineEmits<{ retry: [] }>()
 <template>
   <div class="error" role="alert" :data-error-code="code">
     <p>{{ message }}</p>
-    <button type="button" @click="$emit('retry')">Edit and retry</button>
+    <button type="button" @click="$emit('retry')">{{ messages.streamErrorRetry }}</button>
   </div>
 </template>