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/useArrayReduce.md

@@ -0,0 +1,81 @@
+---
+category: Array
+---
+
+# useArrayReduce
+
+Reactive `Array.reduce`.
+
+## Usage
+
+```ts
+import { useArrayReduce } from '@vueuse/core'
+
+const sum = useArrayReduce([ref(1), ref(2), ref(3)], (sum, val) => sum + val)
+// sum.value: 6
+```
+
+### Use with reactive array
+
+```ts
+import { useArrayReduce } from '@vueuse/core'
+
+const list = reactive([1, 2])
+const sum = useArrayReduce(list, (sum, val) => sum + val)
+
+list.push(3)
+// sum.value: 6
+```
+
+### Use with initialValue
+
+```ts
+import { useArrayReduce } from '@vueuse/core'
+
+const list = reactive([{ num: 1 }, { num: 2 }])
+const sum = useArrayReduce(list, (sum, val) => sum + val.num, 0)
+// sum.value: 3
+```
+
+## Type Declarations
+
+```ts
+export type UseArrayReducer<PV, CV, R> = (
+  previousValue: PV,
+  currentValue: CV,
+  currentIndex: number,
+) => R
+export type UseArrayReduceReturn<T = any> = ComputedRef<T>
+/**
+ * Reactive `Array.reduce`
+ *
+ * @see https://vueuse.org/useArrayReduce
+ * @param list - the array was called upon.
+ * @param reducer - a "reducer" function.
+ *
+ * @returns the value that results from running the "reducer" callback function to completion over the entire array.
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function useArrayReduce<T>(
+  list: MaybeRefOrGetter<MaybeRefOrGetter<T>[]>,
+  reducer: UseArrayReducer<T, T, T>,
+): UseArrayReduceReturn<T>
+/**
+ * Reactive `Array.reduce`
+ *
+ * @see https://vueuse.org/useArrayReduce
+ * @param list - the array was called upon.
+ * @param reducer - a "reducer" function.
+ * @param initialValue - a value to be initialized the first time when the callback is called.
+ *
+ * @returns the value that results from running the "reducer" callback function to completion over the entire array.
+ *
+ * @__NO_SIDE_EFFECTS__
+ */
+export declare function useArrayReduce<T, U>(
+  list: MaybeRefOrGetter<MaybeRefOrGetter<T>[]>,
+  reducer: UseArrayReducer<U, T, U>,
+  initialValue: MaybeRefOrGetter<U>,
+): UseArrayReduceReturn<U>
+```