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/useTrunc.md

@@ -0,0 +1,33 @@
+---
+category: '@Math'
+---
+
+# useTrunc
+
+Reactive `Math.trunc`.
+
+## Usage
+
+```ts
+import { useTrunc } from '@vueuse/math'
+
+const value1 = ref(0.95)
+const value2 = ref(-2.34)
+const result1 = useTrunc(value1) // 0
+const result2 = useTrunc(value2) // -2
+```
+
+## Type Declarations
+
+```ts
+/**
+ * Reactive `Math.trunc`.
+ *
+ * @see https://vueuse.org/useTrunc
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function useTrunc(
+  value: MaybeRefOrGetter<number>,
+): ComputedRef<number>
+```