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/createSharedComposable.md

@@ -0,0 +1,42 @@
+---
+category: State
+related: createGlobalState
+---
+
+# createSharedComposable
+
+Make a composable function usable with multiple Vue instances.
+
+> [!WARNING]
+> When used in a **SSR** environment, `createSharedComposable` will **automatically fallback** to a non-shared version.
+> This means every call will create a fresh instance in SSR to avoid [cross-request state pollution](https://vuejs.org/guide/scaling-up/ssr.html#cross-request-state-pollution).
+
+## Usage
+
+```ts
+import { createSharedComposable, useMouse } from '@vueuse/core'
+
+const useSharedMouse = createSharedComposable(useMouse)
+
+// CompA.vue
+const { x, y } = useSharedMouse()
+
+// CompB.vue - will reuse the previous state and no new event listeners will be registered
+const { x, y } = useSharedMouse()
+```
+
+## Type Declarations
+
+```ts
+export type SharedComposableReturn<T extends AnyFn = AnyFn> = T
+/**
+ * Make a composable function usable with multiple Vue instances.
+ *
+ * @see https://vueuse.org/createSharedComposable
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function createSharedComposable<Fn extends AnyFn>(
+  composable: Fn,
+): SharedComposableReturn<Fn>
+```