Replace hardcoded color values with glass design tokens

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

frontend/src/assets/main.css

@@ -138,7 +138,7 @@ body::before {
 }
 
 .form-field::placeholder {
-  color: #999;
+  color: var(--color-text-muted);
   font-weight: 400;
 }
 

frontend/src/components/CreateEventFab.vue

@@ -18,7 +18,7 @@ import { RouterLink } from 'vue-router'
   width: 56px;
   height: 56px;
   border-radius: 50%;
-  color: #fff;
+  color: var(--color-text-on-gradient);
   display: flex;
   align-items: center;
   justify-content: center;

frontend/src/components/EmptyState.vue

@@ -43,7 +43,7 @@ import { RouterLink } from 'vue-router'
   font-family: inherit;
   font-size: 1rem;
   font-weight: 700;
-  color: #fff;
+  color: var(--color-text-on-gradient);
   text-align: center;
 }
 

frontend/src/components/EventCard.vue

@@ -144,7 +144,7 @@ function onTouchEnd() {
 
 .event-card__badge--organizer {
   background: var(--color-accent);
-  color: #fff;
+  color: var(--color-text-on-gradient);
 }
 
 .event-card__badge--attendee {

frontend/src/views/EventDetailView.vue

@@ -470,7 +470,7 @@ onMounted(fetchEvent)
   font-family: inherit;
   font-size: 1rem;
   font-weight: 700;
-  color: #fff;
+  color: var(--color-text-on-gradient);
   text-align: center;
   border: none;
   cursor: pointer;