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/useCssSupports.md

@@ -0,0 +1,33 @@
+---
+category: Browser
+---
+
+# useCssSupports
+
+SSR compatible and reactive [`CSS.supports`](https://developer.mozilla.org/docs/Web/API/CSS/supports_static).
+
+## Usage
+
+```ts
+import { useCssSupports } from '@vueuse/core'
+
+const { isSupported } = useCssSupports('container-type', 'scroll-state')
+```
+
+## Type Declarations
+
+```ts
+export interface UseCssSupportsOptions extends ConfigurableWindow {
+  ssrValue?: boolean
+}
+export interface UseCssSupportsReturn extends Supportable {}
+export declare function useCssSupports(
+  property: MaybeRefOrGetter<string>,
+  value: MaybeRefOrGetter<string>,
+  options?: UseCssSupportsOptions,
+): UseCssSupportsReturn
+export declare function useCssSupports(
+  conditionText: MaybeRefOrGetter<string>,
+  options?: UseCssSupportsOptions,
+): UseCssSupportsReturn
+```