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/reactiveComputed.md

@@ -0,0 +1,34 @@
+---
+category: Reactivity
+---
+
+# reactiveComputed
+
+Computed reactive object. Instead of returning a ref that `computed` does, `reactiveComputed` returns a reactive object.
+
+## Usage
+
+```ts
+import { reactiveComputed } from '@vueuse/core'
+
+const state = reactiveComputed(() => {
+  return {
+    foo: 'bar',
+    bar: 'baz',
+  }
+})
+
+state.bar // 'baz'
+```
+
+## Type Declarations
+
+```ts
+export type ReactiveComputedReturn<T extends object> = UnwrapNestedRefs<T>
+/**
+ * Computed reactive object.
+ */
+export declare function reactiveComputed<T extends object>(
+  fn: ComputedGetter<T>,
+): ReactiveComputedReturn<T>
+```