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/useCounter.md

@@ -0,0 +1,86 @@
+---
+category: Utilities
+---
+
+# useCounter
+
+Basic counter with utility functions.
+
+## Basic Usage
+
+```ts
+import { useCounter } from '@vueuse/core'
+
+const { count, inc, dec, set, reset } = useCounter()
+```
+
+## Usage with options
+
+```ts
+import { useCounter } from '@vueuse/core'
+
+const { count, inc, dec, set, reset } = useCounter(1, { min: 0, max: 16 })
+```
+
+## Type Declarations
+
+```ts
+export interface UseCounterOptions {
+  min?: number
+  max?: number
+}
+export interface UseCounterReturn {
+  /**
+   * The current value of the counter.
+   */
+  readonly count: Readonly<Ref<number>>
+  /**
+   * Increment the counter.
+   *
+   * @param {number} [delta=1] The number to increment.
+   */
+  inc: (delta?: number) => void
+  /**
+   * Decrement the counter.
+   *
+   * @param {number} [delta=1] The number to decrement.
+   */
+  dec: (delta?: number) => void
+  /**
+   * Get the current value of the counter.
+   */
+  get: () => number
+  /**
+   * Set the counter to a new value.
+   *
+   * @param val The new value of the counter.
+   */
+  set: (val: number) => void
+  /**
+   * Reset the counter to an initial value.
+   */
+  reset: (val?: number) => number
+}
+/**
+ * Basic counter with utility functions.
+ *
+ * @see https://vueuse.org/useCounter
+ * @param [initialValue]
+ * @param options
+ */
+export declare function useCounter(
+  initialValue?: MaybeRef<number>,
+  options?: UseCounterOptions,
+): {
+  count: Readonly<
+    | Ref<number, number>
+    | ShallowRef<number, number>
+    | WritableComputedRef<number, number>
+  >
+  inc: (delta?: number) => number
+  dec: (delta?: number) => number
+  get: () => number
+  set: (val: number) => number
+  reset: (val?: number) => number
+}
+```