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/useSubscription.md

@@ -0,0 +1,33 @@
+---
+category: '@RxJS'
+---
+
+# useSubscription
+
+Use an RxJS [`Subscription`](https://rxjs.dev/guide/subscription) without worrying about unsubscribing from it or creating memory leaks.
+
+## Usage
+
+<!-- TODO: import rxjs error if enable twoslash -->
+
+```ts no-twoslash
+import { useSubscription } from '@vueuse/rxjs'
+import { interval } from 'rxjs'
+
+const count = ref(0)
+
+// useSubscription call unsubscribe method before unmount the component
+useSubscription(
+  interval(1000)
+    .subscribe(() => {
+      count.value++
+      console.log(count)
+    }),
+)
+```
+
+## Type Declarations
+
+```ts
+export declare function useSubscription(subscription: Unsubscribable): void
+```