Raise LoginModal z-index above recipe overlay

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/LoginModal.vue

@@ -119,7 +119,7 @@ async function submit() {
   position: fixed;
   inset: 0;
   background: rgba(0, 0, 0, 0.35);
-  z-index: 5000;
+  z-index: 6000;
   display: flex;
   align-items: center;
   justify-content: center;