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/useSessionStorage.md

@@ -0,0 +1,41 @@
+---
+category: State
+---
+
+# useSessionStorage
+
+Reactive [SessionStorage](https://developer.mozilla.org/en-US/docs/Web/API/Window/sessionStorage).
+
+## Usage
+
+Please refer to `useStorage`.
+
+## Type Declarations
+
+```ts
+export declare function useSessionStorage(
+  key: MaybeRefOrGetter<string>,
+  initialValue: MaybeRefOrGetter<string>,
+  options?: UseStorageOptions<string>,
+): RemovableRef<string>
+export declare function useSessionStorage(
+  key: MaybeRefOrGetter<string>,
+  initialValue: MaybeRefOrGetter<boolean>,
+  options?: UseStorageOptions<boolean>,
+): RemovableRef<boolean>
+export declare function useSessionStorage(
+  key: MaybeRefOrGetter<string>,
+  initialValue: MaybeRefOrGetter<number>,
+  options?: UseStorageOptions<number>,
+): RemovableRef<number>
+export declare function useSessionStorage<T>(
+  key: MaybeRefOrGetter<string>,
+  initialValue: MaybeRefOrGetter<T>,
+  options?: UseStorageOptions<T>,
+): RemovableRef<T>
+export declare function useSessionStorage<T = unknown>(
+  key: MaybeRefOrGetter<string>,
+  initialValue: MaybeRefOrGetter<null>,
+  options?: UseStorageOptions<T>,
+): RemovableRef<T>
+```