feat: Refactor duplicate handling in InterestDuplicateNotificationBanner and update merge API for better access control

components/InterestDuplicateNotificationBanner.vue

@@ -1,6 +1,6 @@
 <template>
-  <!-- Debug: Always show banner for testing -->
   <v-alert
+    v-if="showBanner && duplicateCount > 0"
     type="warning"
     variant="tonal"
     closable
@@ -38,7 +38,7 @@
 const { hasRole } = useAuthorization();
 
 const showBanner = ref(true);
-const duplicateCount = ref(3); // Test value - should show obvious duplicates
+const duplicateCount = ref(0);
 const loading = ref(false);
 
 // Check for duplicates on mount (sales/admin users)
@@ -72,8 +72,7 @@ const checkForDuplicates = async () => {
     }
   } catch (error) {
     console.error('[InterestDuplicateNotification] Failed to check for duplicates:', error);
-    // For debugging, let's set a test count to see if banner shows
-    duplicateCount.value = 2; // Test value to see if banner appears
+    // Silently fail - this is just a notification banner
   } finally {
     loading.value = false;
   }