Optimize auth initialization by using cached middleware state

- Replace API calls with cached auth state from middleware in useAuthorization
- Add fallback to session cache and watchers for auth state updates
- Change initialization from async to synchronous for better performance
- Add DuplicateNotificationBanner component

components/DuplicateNotificationBanner.vue

@@ -0,0 +1,91 @@
+<template>
+  <v-alert
+    v-if="showBanner && duplicateCount > 0"
+    type="warning"
+    variant="tonal"
+    closable
+    @click:close="dismissBanner"
+    class="ma-4"
+  >
+    <template #prepend>
+      <v-icon>mdi-content-duplicate</v-icon>
+    </template>
+    
+    <div class="d-flex align-center justify-space-between">
+      <div>
+        <div class="text-subtitle-1 font-weight-medium">
+          {{ duplicateCount }} duplicate interest record{{ duplicateCount > 1 ? 's' : '' }} detected
+        </div>
+        <div class="text-body-2">
+          Duplicate records can affect data integrity and reporting accuracy.
+        </div>
+      </div>
+      
+      <v-btn
+        color="warning"
+        variant="elevated"
+        size="small"
+        :to="'/dashboard/admin/duplicates'"
+        prepend-icon="mdi-wrench"
+      >
+        Clean Up Duplicates
+      </v-btn>
+    </div>
+  </v-alert>
+</template>
+
+<script setup>
+const { isAdmin } = useAuthorization();
+
+const showBanner = ref(true);
+const duplicateCount = ref(0);
+const loading = ref(false);
+
+// Check for duplicates on mount (admin only)
+const checkForDuplicates = async () => {
+  if (!isAdmin() || loading.value) return;
+  
+  try {
+    loading.value = true;
+    const response = await $fetch('/api/admin/duplicates/find', {
+      method: 'POST',
+      body: { threshold: 80 }
+    });
+    
+    if (response.success && response.data?.duplicateGroups) {
+      duplicateCount.value = response.data.duplicateGroups.length;
+    }
+  } catch (error) {
+    console.error('[DuplicateNotification] Failed to check for duplicates:', error);
+    // Silently fail - this is just a notification banner
+  } finally {
+    loading.value = false;
+  }
+};
+
+// Dismiss the banner for this session
+const dismissBanner = () => {
+  showBanner.value = false;
+  // Store dismissal in session storage
+  if (process.client) {
+    sessionStorage.setItem('duplicates-banner-dismissed', 'true');
+  }
+};
+
+// Check if banner was already dismissed this session
+onMounted(() => {
+  if (process.client) {
+    const dismissed = sessionStorage.getItem('duplicates-banner-dismissed');
+    if (dismissed === 'true') {
+      showBanner.value = false;
+      return;
+    }
+  }
+  
+  // Only check for duplicates if user is admin
+  if (isAdmin()) {
+    // Small delay to let other components load first
+    setTimeout(checkForDuplicates, 2000);
+  }
+});
+</script>