fix: use StorageSerializers.set + triggerRef for Set reactivity

- Use @vueuse/core StorageSerializers.set for proper Set serialization
- Add triggerRef after Set mutations (add/delete/clear) for Vue reactivity
- Mock useStorage in test setup to avoid localStorage state pollution

test/setup.ts

@@ -1,4 +1,5 @@
 import { vi } from 'vitest'
+import { ref } from 'vue'
 import 'fake-indexeddb/auto'
 
 // Mock useScriptGoogleTagManager globally
@@ -10,6 +11,17 @@ vi.stubGlobal('useScriptGoogleTagManager', () => ({
   },
 }))
 
+// Mock @vueuse/core useStorage to use plain ref (no localStorage) in tests
+vi.mock('@vueuse/core', async () => {
+  const actual = await vi.importActual('@vueuse/core')
+  return {
+    ...actual,
+    useStorage: (_key: string, defaultValue: unknown) => ref(
+      typeof defaultValue === 'function' ? defaultValue() : defaultValue,
+    ),
+  }
+})
+
 // Mock onMounted to prevent Vue warnings in tests
 vi.mock('vue', async () => {
   const actual = await vi.importActual('vue')