fix(ui-copy): copyText utility with execCommand fallback — navigator.clipboard is gated by Secure Context (HTTPS-only) and is undefined on plain-HTTP self-hosted deployments. Apply to ExtensionKeyBar + BrowserExtensionCard.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/credentials/ExtensionKeyBar.vue

@@ -28,6 +28,7 @@
 <script setup>
 import { onMounted, ref } from 'vue'
 import { useCredentialsStore } from '../../stores/credentials.js'
+import { copyText } from '../../utils/clipboard.js'
 
 const store = useCredentialsStore()
 const showRotateConfirm = ref(false)
@@ -37,7 +38,7 @@ onMounted(() => store.loadKey())
 async function copyKey() {
   if (!store.extensionKey) return
   try {
-    await navigator.clipboard.writeText(store.extensionKey)
+    await copyText(store.extensionKey)
     globalThis.window?.__fcToast?.({ text: 'Copied', type: 'success' })
   } catch {
     globalThis.window?.__fcToast?.({ text: 'Copy failed', type: 'error' })