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/useIdle.md

@@ -0,0 +1,88 @@
+---
+category: Sensors
+---
+
+# useIdle
+
+Tracks whether the user is being inactive.
+
+## Usage
+
+```ts
+import { useIdle } from '@vueuse/core'
+
+const { idle, lastActive } = useIdle(5 * 60 * 1000) // 5 min
+
+console.log(idle.value) // true or false
+```
+
+Programatically resetting:
+
+```ts
+import { useCounter, useIdle } from '@vueuse/core'
+import { watch } from 'vue'
+
+const { inc, count } = useCounter()
+
+const { idle, lastActive, reset } = useIdle(5 * 60 * 1000) // 5 min
+
+watch(idle, (idleValue) => {
+  if (idleValue) {
+    inc()
+    console.log(`Triggered ${count.value} times`)
+    reset() // restarts the idle timer. Does not change lastActive value
+  }
+})
+```
+
+## Component Usage
+
+```vue
+<template>
+  <UseIdle v-slot="{ idle }" :timeout="5 * 60 * 1000">
+    Is Idle: {{ idle }}
+  </UseIdle>
+</template>
+```
+
+## Type Declarations
+
+```ts
+export interface UseIdleOptions
+  extends ConfigurableWindow, ConfigurableEventFilter {
+  /**
+   * Event names that listen to for detected user activity
+   *
+   * @default ['mousemove', 'mousedown', 'resize', 'keydown', 'touchstart', 'wheel']
+   */
+  events?: WindowEventName[]
+  /**
+   * Listen for document visibility change
+   *
+   * @default true
+   */
+  listenForVisibilityChange?: boolean
+  /**
+   * Initial state of the ref idle
+   *
+   * @default false
+   */
+  initialState?: boolean
+}
+export interface UseIdleReturn extends Stoppable {
+  idle: ShallowRef<boolean>
+  lastActive: ShallowRef<number>
+  reset: () => void
+}
+/**
+ * Tracks whether the user is being inactive.
+ *
+ * @see https://vueuse.org/useIdle
+ * @param timeout default to 1 minute
+ * @param options IdleOptions
+ */
+export declare function useIdle(
+  timeout?: number,
+  options?: UseIdleOptions,
+): UseIdleReturn
+```