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/useTimeoutFn.md

@@ -0,0 +1,51 @@
+---
+category: Animation
+---
+
+# useTimeoutFn
+
+Wrapper for `setTimeout` with controls.
+
+## Usage
+
+```ts
+import { useTimeoutFn } from '@vueuse/core'
+
+const { isPending, start, stop } = useTimeoutFn(() => {
+  /* ... */
+}, 3000)
+```
+
+## Type Declarations
+
+```ts
+export interface UseTimeoutFnOptions {
+  /**
+   * Start the timer immediately
+   *
+   * @default true
+   */
+  immediate?: boolean
+  /**
+   * Execute the callback immediately after calling `start`
+   *
+   * @default false
+   */
+  immediateCallback?: boolean
+}
+export type UseTimeoutFnReturn<CallbackFn extends AnyFn> = Stoppable<
+  Parameters<CallbackFn> | []
+>
+/**
+ * Wrapper for `setTimeout` with controls.
+ *
+ * @param cb
+ * @param interval
+ * @param options
+ */
+export declare function useTimeoutFn<CallbackFn extends AnyFn>(
+  cb: CallbackFn,
+  interval: MaybeRefOrGetter<number>,
+  options?: UseTimeoutFnOptions,
+): UseTimeoutFnReturn<CallbackFn>
+```