docs: add advanced skills for Vitest, Pinia, and Vue built-ins

Add comprehensive reference documentation for:
- Vitest: environments, projects/workspaces, type testing, vi utilities
- Pinia: HMR, Nuxt integration, SSR setup
- Vue: built-in components (Transition, Teleport, Suspense, KeepAlive) and advanced directives

.agents/skills/vueuse-functions/references/useWindowScroll.md

@@ -0,0 +1,46 @@
+---
+category: Elements
+---
+
+# useWindowScroll
+
+Reactive window scroll
+
+## Usage
+
+```vue
+<script setup lang="ts">
+import { useWindowScroll } from '@vueuse/core'
+
+const { x, y } = useWindowScroll()
+</script>
+
+<template>
+  <div>
+    read current x, y scroll: {{ x }}, {{ y }}
+  </div>
+  <button @click="x = 100">
+    scroll X to 100
+  </button>
+  <button @click="y = 100">
+    scroll Y to 100
+  </button>
+</template>
+```
+
+## Type Declarations
+
+```ts
+export interface UseWindowScrollOptions
+  extends ConfigurableWindow, UseScrollOptions {}
+export interface UseWindowScrollReturn extends UseScrollReturn {}
+/**
+ * Reactive window scroll.
+ *
+ * @see https://vueuse.org/useWindowScroll
+ * @param options
+ */
+export declare function useWindowScroll(
+  options?: UseWindowScrollOptions,
+): UseWindowScrollReturn
+```