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/useFileSystemAccess.md

@@ -0,0 +1,161 @@
+---
+category: Browser
+---
+
+# useFileSystemAccess
+
+Create and read and write local files with [FileSystemAccessAPI](https://developer.mozilla.org/en-US/docs/Web/API/File_System_Access_API)
+
+## Usage
+
+```ts
+import { useFileSystemAccess } from '@vueuse/core'
+
+const {
+  isSupported,
+  data,
+  file,
+  fileName,
+  fileMIME,
+  fileSize,
+  fileLastModified,
+  create,
+  open,
+  save,
+  saveAs,
+  updateData
+} = useFileSystemAccess()
+```
+
+## Type Declarations
+
+```ts
+/**
+ * window.showOpenFilePicker parameters
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/window/showOpenFilePicker#parameters
+ */
+export interface FileSystemAccessShowOpenFileOptions {
+  multiple?: boolean
+  types?: Array<{
+    description?: string
+    accept: Record<string, string[]>
+  }>
+  excludeAcceptAllOption?: boolean
+}
+/**
+ * window.showSaveFilePicker parameters
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/window/showSaveFilePicker#parameters
+ */
+export interface FileSystemAccessShowSaveFileOptions {
+  suggestedName?: string
+  types?: Array<{
+    description?: string
+    accept: Record<string, string[]>
+  }>
+  excludeAcceptAllOption?: boolean
+}
+/**
+ * FileHandle
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemFileHandle
+ */
+export interface FileSystemFileHandle {
+  getFile: () => Promise<File>
+  createWritable: () => FileSystemWritableFileStream
+}
+/**
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream
+ */
+interface FileSystemWritableFileStream extends WritableStream {
+  /**
+   * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream/write
+   */
+  write: FileSystemWritableFileStreamWrite
+  /**
+   * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream/seek
+   */
+  seek: (position: number) => Promise<void>
+  /**
+   * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream/truncate
+   */
+  truncate: (size: number) => Promise<void>
+}
+/**
+ * FileStream.write
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream/write
+ */
+interface FileSystemWritableFileStreamWrite {
+  (data: string | BufferSource | Blob): Promise<void>
+  (options: {
+    type: "write"
+    position: number
+    data: string | BufferSource | Blob
+  }): Promise<void>
+  (options: { type: "seek"; position: number }): Promise<void>
+  (options: { type: "truncate"; size: number }): Promise<void>
+}
+/**
+ * FileStream.write
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/FileSystemWritableFileStream/write
+ */
+export type FileSystemAccessWindow = Window & {
+  showSaveFilePicker: (
+    options: FileSystemAccessShowSaveFileOptions,
+  ) => Promise<FileSystemFileHandle>
+  showOpenFilePicker: (
+    options: FileSystemAccessShowOpenFileOptions,
+  ) => Promise<FileSystemFileHandle[]>
+}
+export type UseFileSystemAccessCommonOptions = Pick<
+  FileSystemAccessShowOpenFileOptions,
+  "types" | "excludeAcceptAllOption"
+>
+export type UseFileSystemAccessShowSaveFileOptions = Pick<
+  FileSystemAccessShowSaveFileOptions,
+  "suggestedName"
+>
+export type UseFileSystemAccessOptions = ConfigurableWindow &
+  UseFileSystemAccessCommonOptions & {
+    /**
+     * file data type
+     */
+    dataType?: MaybeRefOrGetter<"Text" | "ArrayBuffer" | "Blob">
+  }
+/**
+ * Create and read and write local files.
+ * @see https://vueuse.org/useFileSystemAccess
+ */
+export declare function useFileSystemAccess(): UseFileSystemAccessReturn<
+  string | ArrayBuffer | Blob
+>
+export declare function useFileSystemAccess(
+  options: UseFileSystemAccessOptions & {
+    dataType: "Text"
+  },
+): UseFileSystemAccessReturn<string>
+export declare function useFileSystemAccess(
+  options: UseFileSystemAccessOptions & {
+    dataType: "ArrayBuffer"
+  },
+): UseFileSystemAccessReturn<ArrayBuffer>
+export declare function useFileSystemAccess(
+  options: UseFileSystemAccessOptions & {
+    dataType: "Blob"
+  },
+): UseFileSystemAccessReturn<Blob>
+export declare function useFileSystemAccess(
+  options: UseFileSystemAccessOptions,
+): UseFileSystemAccessReturn<string | ArrayBuffer | Blob>
+export interface UseFileSystemAccessReturn<T = string> extends Supportable {
+  data: ShallowRef<T | undefined>
+  file: ShallowRef<File | undefined>
+  fileName: ComputedRef<string>
+  fileMIME: ComputedRef<string>
+  fileSize: ComputedRef<number>
+  fileLastModified: ComputedRef<number>
+  open: (_options?: UseFileSystemAccessCommonOptions) => Awaitable<void>
+  create: (_options?: UseFileSystemAccessShowSaveFileOptions) => Awaitable<void>
+  save: (_options?: UseFileSystemAccessShowSaveFileOptions) => Awaitable<void>
+  saveAs: (_options?: UseFileSystemAccessShowSaveFileOptions) => Awaitable<void>
+  updateData: () => Awaitable<void>
+}
+```