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/useBase64.md

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+---
+category: Utilities
+---
+
+# useBase64
+
+Reactive base64 transforming. Supports plain text, buffer, files, canvas, objects, maps, sets and images.
+
+## Usage
+
+```ts
+import { useBase64 } from '@vueuse/core'
+import { shallowRef } from 'vue'
+
+const text = shallowRef('')
+
+const { base64, promise, execute } = useBase64(text)
+```
+
+### Supported Input Types
+
+- `string` - Plain text
+- `Blob` - File or blob data
+- `ArrayBuffer` - Binary data
+- `HTMLCanvasElement` - Canvas element
+- `HTMLImageElement` - Image element
+- `Object` / `Array` / `Map` / `Set` - Serialized to JSON
+
+### Return Values
+
+| Property  | Description                               |
+| --------- | ----------------------------------------- |
+| `base64`  | The resulting base64 string               |
+| `promise` | The promise of the current transformation |
+| `execute` | Manually trigger the transformation       |
+
+### Data URL Format
+
+By default, the output is in Data URL format (e.g., `data:text/plain;base64,...`). Set `dataUrl: false` to get raw base64.
+
+```ts
+const { base64 } = useBase64(text, { dataUrl: false })
+// Returns raw base64 without the data URL prefix
+```
+
+### Canvas and Image Options
+
+When transforming canvas or image elements, you can specify the MIME type and quality.
+
+```ts
+const canvas = document.querySelector('canvas')
+
+const { base64 } = useBase64(canvas, {
+  type: 'image/jpeg', // MIME type
+  quality: 0.8, // Image quality (0-1, for jpeg/webp)
+})
+```
+
+### Custom Serializer
+
+For objects, arrays, maps and sets, you can provide a custom serializer. Otherwise, the data will be serialized using `JSON.stringify` (maps are converted to objects, sets to arrays).
+
+```ts
+const data = shallowRef({ foo: 'bar' })
+
+const { base64 } = useBase64(data, {
+  serializer: v => JSON.stringify(v, null, 2),
+})
+```
+
+## Type Declarations
+
+```ts
+export interface UseBase64Options {
+  /**
+   * Output as Data URL format
+   *
+   * @default true
+   */
+  dataUrl?: boolean
+}
+export interface ToDataURLOptions extends UseBase64Options {
+  /**
+   * MIME type
+   */
+  type?: string | undefined
+  /**
+   * Image quality of jpeg or webp
+   */
+  quality?: any
+}
+export interface UseBase64ObjectOptions<T> extends UseBase64Options {
+  serializer?: (v: T) => string
+}
+export interface UseBase64Return {
+  base64: ShallowRef<string>
+  promise: ShallowRef<Promise<string>>
+  execute: () => Promise<string>
+}
+export declare function useBase64(
+  target: MaybeRefOrGetter<string | undefined>,
+  options?: UseBase64Options,
+): UseBase64Return
+export declare function useBase64(
+  target: MaybeRefOrGetter<Blob | undefined>,
+  options?: UseBase64Options,
+): UseBase64Return
+export declare function useBase64(
+  target: MaybeRefOrGetter<ArrayBuffer | undefined>,
+  options?: UseBase64Options,
+): UseBase64Return
+export declare function useBase64(
+  target: MaybeRefOrGetter<HTMLCanvasElement | undefined>,
+  options?: ToDataURLOptions,
+): UseBase64Return
+export declare function useBase64(
+  target: MaybeRefOrGetter<HTMLImageElement | undefined>,
+  options?: ToDataURLOptions,
+): UseBase64Return
+export declare function useBase64<T extends Record<string, unknown>>(
+  target: MaybeRefOrGetter<T>,
+  options?: UseBase64ObjectOptions<T>,
+): UseBase64Return
+export declare function useBase64<T extends Map<string, unknown>>(
+  target: MaybeRefOrGetter<T>,
+  options?: UseBase64ObjectOptions<T>,
+): UseBase64Return
+export declare function useBase64<T extends Set<unknown>>(
+  target: MaybeRefOrGetter<T>,
+  options?: UseBase64ObjectOptions<T>,
+): UseBase64Return
+export declare function useBase64<T>(
+  target: MaybeRefOrGetter<T[]>,
+  options?: UseBase64ObjectOptions<T[]>,
+): UseBase64Return
+```