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/useUserMedia.md

@@ -0,0 +1,96 @@
+---
+category: Sensors
+related: useDevicesList, usePermission
+---
+
+# useUserMedia
+
+Reactive [`mediaDevices.getUserMedia`](https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia) streaming.
+
+## Usage
+
+```vue
+<script setup lang="ts">
+import { useUserMedia } from '@vueuse/core'
+import { useTemplateRef, watchEffect } from 'vue'
+
+const { stream, start } = useUserMedia()
+start()
+
+const videoRef = useTemplateRef('video')
+watchEffect(() => {
+  // preview on a video element
+  videoRef.value.srcObject = stream.value
+})
+</script>
+
+<template>
+  <video ref="video" />
+</template>
+```
+
+### Devices
+
+```ts
+import { useDevicesList, useUserMedia } from '@vueuse/core'
+import { computed, reactive } from 'vue'
+
+const {
+  videoInputs: cameras,
+  audioInputs: microphones,
+} = useDevicesList({
+  requestPermissions: true,
+})
+const currentCamera = computed(() => cameras.value[0]?.deviceId)
+const currentMicrophone = computed(() => microphones.value[0]?.deviceId)
+
+const { stream } = useUserMedia({
+  constraints: reactive({
+    video: { deviceId: currentCamera },
+    audio: { deviceId: currentMicrophone, }
+  })
+})
+```
+
+## Type Declarations
+
+```ts
+export interface UseUserMediaOptions extends ConfigurableNavigator {
+  /**
+   * If the stream is enabled
+   * @default false
+   */
+  enabled?: MaybeRef<boolean>
+  /**
+   * Recreate stream when deviceIds or constraints changed
+   *
+   * @default true
+   */
+  autoSwitch?: MaybeRef<boolean>
+  /**
+   * MediaStreamConstraints to be applied to the requested MediaStream
+   * If provided, the constraints will override videoDeviceId and audioDeviceId
+   *
+   * @default {}
+   */
+  constraints?: MaybeRef<MediaStreamConstraints>
+}
+export interface UseUserMediaReturn extends Supportable {
+  stream: Ref<MediaStream | undefined>
+  start: () => Promise<MediaStream | undefined>
+  stop: () => void
+  restart: () => Promise<MediaStream | undefined>
+  constraints: Ref<MediaStreamConstraints | undefined>
+  enabled: ShallowRef<boolean>
+  autoSwitch: ShallowRef<boolean>
+}
+/**
+ * Reactive `mediaDevices.getUserMedia` streaming
+ *
+ * @see https://vueuse.org/useUserMedia
+ * @param options
+ */
+export declare function useUserMedia(
+  options?: UseUserMediaOptions,
+): UseUserMediaReturn
+```