Apply glassmorphism to BottomSheet and RSVP bar status

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

frontend/src/components/RsvpBar.vue

@@ -78,13 +78,16 @@ defineEmits<{
   align-items: center;
   justify-content: center;
   gap: var(--spacing-xs);
-  background: var(--color-card);
+  background: linear-gradient(135deg, var(--color-glass-strong) 0%, var(--color-glass-subtle) 100%);
+  border: 1px solid var(--color-glass-border);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
   border-radius: var(--radius-card);
   padding: var(--spacing-md) var(--spacing-lg);
   box-shadow: var(--shadow-card);
   font-weight: 600;
   font-size: 0.95rem;
-  color: var(--color-text);
+  color: var(--color-text-on-gradient);
 }
 
 .rsvp-bar__check {