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/useThrottleFn.md

@@ -0,0 +1,57 @@
+---
+category: Utilities
+related: refThrottled, refDebounced, useDebounceFn
+---
+
+# useThrottleFn
+
+Throttle execution of a function. Especially useful for rate limiting execution of handlers on events like resize and scroll.
+
+> Throttle is a spring that throws balls: after a ball flies out it needs some time to shrink back, so it cannot throw any more balls unless it's ready.
+
+## Usage
+
+```ts
+import { useThrottleFn } from '@vueuse/core'
+
+const throttledFn = useThrottleFn(() => {
+  // do something, it will be called at most 1 time per second
+}, 1000)
+
+useEventListener(window, 'resize', throttledFn)
+```
+
+## Recommended Reading
+
+- [**Debounce vs Throttle**: Definitive Visual Guide](https://kettanaito.com/blog/debounce-vs-throttle)
+
+## Type Declarations
+
+```ts
+/**
+ * Throttle execution of a function. Especially useful for rate limiting
+ * execution of handlers on events like resize and scroll.
+ *
+ * @param   fn             A function to be executed after delay milliseconds. The `this` context and all arguments are passed through, as-is,
+ *                                    to `callback` when the throttled-function is executed.
+ * @param   ms             A zero-or-greater delay in milliseconds. For event callbacks, values around 100 or 250 (or even higher) are most useful.
+ *                                    (default value: 200)
+ *
+ * @param [trailing] if true, call fn again after the time is up (default value: false)
+ *
+ * @param [leading] if true, call fn on the leading edge of the ms timeout (default value: true)
+ *
+ * @param [rejectOnCancel] if true, reject the last call if it's been cancel (default value: false)
+ *
+ * @return  A new, throttled, function.
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function useThrottleFn<T extends FunctionArgs>(
+  fn: T,
+  ms?: MaybeRefOrGetter<number>,
+  trailing?: boolean,
+  leading?: boolean,
+  rejectOnCancel?: boolean,
+): PromisifyFn<T>
+```