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/useInterval.md

@@ -0,0 +1,112 @@
+---
+category: Animation
+---
+
+# useInterval
+
+Reactive counter that increases on every interval.
+
+## Usage
+
+```ts
+import { useInterval } from '@vueuse/core'
+
+// count will increase every 200ms
+const counter = useInterval(200)
+```
+
+### With Controls
+
+```ts
+import { useInterval } from '@vueuse/core'
+
+const { counter, reset, pause, resume, isActive } = useInterval(200, {
+  controls: true,
+})
+
+// Reset counter to 0
+reset()
+
+// Pause/resume the interval
+pause()
+resume()
+```
+
+### Options
+
+| Option      | Type                      | Default | Description                                                |
+| ----------- | ------------------------- | ------- | ---------------------------------------------------------- |
+| `controls`  | `boolean`                 | `false` | Expose `pause`, `resume`, `reset`, and `isActive` controls |
+| `immediate` | `boolean`                 | `true`  | Start the interval immediately                             |
+| `callback`  | `(count: number) => void` | —       | Called on every interval with the current count            |
+
+### Reactive Interval
+
+The interval can be reactive:
+
+```ts
+import { useInterval } from '@vueuse/core'
+
+const intervalMs = ref(1000)
+const counter = useInterval(intervalMs)
+
+// Change the interval dynamically
+intervalMs.value = 500
+```
+
+### Callback on Every Interval
+
+```ts
+import { useInterval } from '@vueuse/core'
+
+useInterval(1000, {
+  callback: (count) => {
+    console.log(`Tick ${count}`)
+  },
+})
+```
+
+## Type Declarations
+
+```ts
+export interface UseIntervalOptions<Controls extends boolean> {
+  /**
+   * Expose more controls
+   *
+   * @default false
+   */
+  controls?: Controls
+  /**
+   * Execute the update immediately on calling
+   *
+   * @default true
+   */
+  immediate?: boolean
+  /**
+   * Callback on every interval
+   */
+  callback?: (count: number) => void
+}
+export interface UseIntervalControls {
+  counter: ShallowRef<number>
+  reset: () => void
+}
+export type UseIntervalReturn =
+  | Readonly<ShallowRef<number>>
+  | Readonly<UseIntervalControls & Pausable>
+/**
+ * Reactive counter increases on every interval
+ *
+ * @see https://vueuse.org/useInterval
+ * @param interval
+ * @param options
+ */
+export declare function useInterval(
+  interval?: MaybeRefOrGetter<number>,
+  options?: UseIntervalOptions<false>,
+): Readonly<ShallowRef<number>>
+export declare function useInterval(
+  interval: MaybeRefOrGetter<number>,
+  options: UseIntervalOptions<true>,
+): Readonly<UseIntervalControls & Pausable>
+```