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/unrefElement.md

@@ -0,0 +1,54 @@
+---
+category: Component
+---
+
+# unrefElement
+
+Retrieves the underlying DOM element from a Vue ref or component instance
+
+## Usage
+
+```vue
+<script setup lang="ts">
+import { unrefElement } from '@vueuse/core'
+import { onMounted, useTemplateRef } from 'vue'
+
+const div = useTemplateRef('div') // will be bound to the <div> element
+const hello = useTemplateRef('hello') // will be bound to the HelloWorld Component
+
+onMounted(() => {
+  console.log(unrefElement(div)) // the <div> element
+  console.log(unrefElement(hello)) // the root element of the HelloWorld Component
+})
+</script>
+
+<template>
+  <div ref="div" />
+  <HelloWorld ref="hello" />
+</template>
+```
+
+## Type Declarations
+
+```ts
+export type VueInstance = ComponentPublicInstance
+export type MaybeElementRef<T extends MaybeElement = MaybeElement> = MaybeRef<T>
+export type MaybeComputedElementRef<T extends MaybeElement = MaybeElement> =
+  MaybeRefOrGetter<T>
+export type MaybeElement =
+  | HTMLElement
+  | SVGElement
+  | VueInstance
+  | undefined
+  | null
+export type UnRefElementReturn<T extends MaybeElement = MaybeElement> =
+  T extends VueInstance ? Exclude<MaybeElement, VueInstance> : T | undefined
+/**
+ * Get the dom element of a ref of element or Vue component instance
+ *
+ * @param elRef
+ */
+export declare function unrefElement<T extends MaybeElement>(
+  elRef: MaybeComputedElementRef<T>,
+): UnRefElementReturn<T>
+```