fix(settings): fallback clipboard copy for http dev environments

navigator.clipboard.writeText() requires a secure context (HTTPS) and
silently fails on http://. Add an execCommand fallback so the API key
copy button works on non-secure dev instances.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/SettingsView.vue

@@ -89,7 +89,20 @@ async function revokeApiKey(id: number) {
 }
 
 async function copyApiKey() {
-  await navigator.clipboard.writeText(newKeyValue.value);
+  try {
+    await navigator.clipboard.writeText(newKeyValue.value);
+  } catch {
+    // Fallback for http (non-secure) contexts where clipboard API is unavailable
+    const ta = document.createElement('textarea');
+    ta.value = newKeyValue.value;
+    ta.style.position = 'fixed';
+    ta.style.opacity = '0';
+    document.body.appendChild(ta);
+    ta.focus();
+    ta.select();
+    document.execCommand('copy');
+    document.body.removeChild(ta);
+  }
   apiKeyCopied.value = true;
   setTimeout(() => { apiKeyCopied.value = false; }, 2000);
 }