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/useArrayFind.md

@@ -0,0 +1,50 @@
+---
+category: Array
+---
+
+# useArrayFind
+
+Reactive `Array.find`.
+
+## Usage
+
+```ts
+import { useArrayFind } from '@vueuse/core'
+
+const list = [ref(1), ref(-1), ref(2)]
+const positive = useArrayFind(list, val => val > 0)
+// positive.value: 1
+```
+
+### Use with reactive array
+
+```ts
+import { useArrayFind } from '@vueuse/core'
+
+const list = reactive([-1, -2])
+const positive = useArrayFind(list, val => val > 0)
+// positive.value: undefined
+list.push(1)
+// positive.value: 1
+```
+
+## Type Declarations
+
+```ts
+export type UseArrayFindReturn<T = any> = ComputedRef<T | undefined>
+/**
+ * Reactive `Array.find`
+ *
+ * @see https://vueuse.org/useArrayFind
+ * @param list - the array was called upon.
+ * @param fn - a function to test each element.
+ *
+ * @returns the first element in the array that satisfies the provided testing function. Otherwise, undefined is returned.
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function useArrayFind<T>(
+  list: MaybeRefOrGetter<MaybeRefOrGetter<T>[]>,
+  fn: (element: T, index: number, array: MaybeRefOrGetter<T>[]) => boolean,
+): UseArrayFindReturn<T>
+```