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/useTitle.md

@@ -0,0 +1,115 @@
+---
+category: Browser
+---
+
+# useTitle
+
+Reactive document title.
+
+::: warning
+This composable isn't compatible with SSR.
+:::
+
+## Usage
+
+```ts
+import { useTitle } from '@vueuse/core'
+
+const title = useTitle()
+console.log(title.value) // print current title
+title.value = 'Hello' // change current title
+```
+
+Set initial title immediately:
+
+```ts
+import { useTitle } from '@vueuse/core'
+// ---cut---
+const title = useTitle('New Title')
+```
+
+Pass a `ref` and the title will be updated when the source ref changes:
+
+```ts
+import { useTitle } from '@vueuse/core'
+import { shallowRef } from 'vue'
+
+const messages = shallowRef(0)
+
+const title = computed(() => {
+  return !messages.value ? 'No message' : `${messages.value} new messages`
+})
+
+useTitle(title) // document title will match with the ref "title"
+```
+
+Pass an optional template tag [Vue Meta Title Template](https://vue-meta.nuxtjs.org/guide/metainfo.html) to update the title to be injected into this template:
+
+```ts
+import { useTitle } from '@vueuse/core'
+// ---cut---
+const title = useTitle('New Title', {
+  titleTemplate: '%s | My Awesome Website'
+})
+```
+
+::: warning
+`observe` is incompatible with `titleTemplate`.
+:::
+
+## Type Declarations
+
+```ts
+export type UseTitleOptionsBase = {
+  /**
+   * Restore the original title when unmounted
+   * @param originTitle original title
+   * @returns restored title
+   */
+  restoreOnUnmount?:
+    | false
+    | ((
+        originalTitle: string,
+        currentTitle: string,
+      ) => string | null | undefined)
+} & (
+  | {
+      /**
+       * Observe `document.title` changes using MutationObserve
+       * Cannot be used together with `titleTemplate` option.
+       *
+       * @default false
+       */
+      observe?: boolean
+    }
+  | {
+      /**
+       * The template string to parse the title (e.g., '%s | My Website')
+       * Cannot be used together with `observe` option.
+       *
+       * @default '%s'
+       */
+      titleTemplate?: MaybeRef<string> | ((title: string) => string)
+    }
+)
+export type UseTitleOptions = ConfigurableDocument & UseTitleOptionsBase
+export type UseTitleReturn =
+  | ComputedRef<string | null | undefined>
+  | Ref<string | null | undefined>
+/**
+ * Reactive document title.
+ *
+ * @see https://vueuse.org/useTitle
+ * @param newTitle
+ * @param options
+ * @description It's not SSR compatible. Your value will be applied only on client-side.
+ */
+export declare function useTitle(
+  newTitle: ReadonlyRefOrGetter<string | null | undefined>,
+  options?: UseTitleOptions,
+): ComputedRef<string | null | undefined>
+export declare function useTitle(
+  newTitle?: MaybeRef<string | null | undefined>,
+  options?: UseTitleOptions,
+): Ref<string | null | undefined>
+```