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/usePreferredReducedTransparency.md

@@ -0,0 +1,42 @@
+---
+category: Browser
+---
+
+# usePreferredReducedTransparency
+
+Reactive [prefers-reduced-transparency](https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-transparency) media query.
+
+## Usage
+
+```ts
+import { usePreferredReducedTransparency } from '@vueuse/core'
+
+const preferredTransparency = usePreferredReducedTransparency()
+```
+
+## Component Usage
+
+```vue
+<template>
+  <UsePreferredReducedTransparency v-slot="{ transparency }">
+    Preferred Reduced transparency: {{ transparency }}
+  </UsePreferredReducedTransparency>
+</template>
+```
+
+## Type Declarations
+
+```ts
+export type ReducedTransparencyType = "reduce" | "no-preference"
+/**
+ * Reactive prefers-reduced-transparency media query.
+ *
+ * @see https://vueuse.org/usePreferredReducedTransparency
+ * @param [options]
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function usePreferredReducedTransparency(
+  options?: ConfigurableWindow,
+): ComputedRef<ReducedTransparencyType>
+```