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/useCached.md

@@ -0,0 +1,52 @@
+---
+category: Utilities
+---
+
+# useCached
+
+Cache a ref with a custom comparator.
+
+## Usage
+
+```ts
+import { useCached } from '@vueuse/core'
+import { shallowRef } from 'vue'
+
+interface Data {
+  value: number
+  extra: number
+}
+
+const source = shallowRef<Data>({ value: 42, extra: 0 })
+const cached = useCached(source, (a, b) => a.value === b.value)
+
+source.value = {
+  value: 42,
+  extra: 1,
+}
+
+console.log(cached.value) // { value: 42, extra: 0 }
+
+source.value = {
+  value: 43,
+  extra: 1,
+}
+
+console.log(cached.value) // { value: 43, extra: 1 }
+```
+
+## Type Declarations
+
+```ts
+export interface UseCachedOptions<D extends boolean = true>
+  extends ConfigurableDeepRefs<D>, WatchOptions {}
+export declare function useCached<T, D extends boolean = true>(
+  refValue: Ref<T>,
+  comparator?: (a: T, b: T) => boolean,
+  options?: UseCachedOptions<D>,
+): UseCachedReturn<T, D>
+export type UseCachedReturn<
+  T = any,
+  D extends boolean = true,
+> = ShallowOrDeepRef<T, D>
+```