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/useKeyModifier.md

@@ -0,0 +1,87 @@
+---
+category: Sensors
+---
+
+# useKeyModifier
+
+Reactive [Modifier State](https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/getModifierState). Tracks state of any of the [supported modifiers](https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/getModifierState#browser_compatibility) - see Browser Compatibility notes.
+
+<CourseLink href="https://vueschool.io/lessons/alt-drag-to-clone-tasks?friend=vueuse">Learn useKeyModifier with this FREE video lesson from Vue School!</CourseLink>
+
+## Usage
+
+```ts
+import { useKeyModifier } from '@vueuse/core'
+
+const capsLockState = useKeyModifier('CapsLock')
+
+console.log(capsLockState.value)
+```
+
+## Events
+
+You can customize which events will prompt the state to update. By default, these are `mouseup`, `mousedown`, `keyup`, `keydown`. To customize these events:
+
+```ts
+import { useKeyModifier } from '@vueuse/core'
+
+const capsLockState = useKeyModifier('CapsLock', { events: ['mouseup', 'mousedown'] })
+
+console.log(capsLockState) // null
+
+// Caps Lock turned on with key press
+console.log(capsLockState) // null
+
+// Mouse button clicked
+console.log(capsLockState) // true
+```
+
+## Initial State
+
+By default, the returned ref will be `Ref<null>` until the first event is received. You can explicitly pass the initial state to it via:
+
+```ts
+import { useKeyModifier } from '@vueuse/core'
+// ---cut---
+const capsLockState1 = useKeyModifier('CapsLock') // Ref<boolean | null>
+const capsLockState2 = useKeyModifier('CapsLock', { initial: false }) // Ref<boolean>
+```
+
+## Type Declarations
+
+```ts
+export type KeyModifier =
+  | "Alt"
+  | "AltGraph"
+  | "CapsLock"
+  | "Control"
+  | "Fn"
+  | "FnLock"
+  | "Meta"
+  | "NumLock"
+  | "ScrollLock"
+  | "Shift"
+  | "Symbol"
+  | "SymbolLock"
+export interface UseModifierOptions<Initial> extends ConfigurableDocument {
+  /**
+   * Event names that will prompt update to modifier states
+   *
+   * @default ['mousedown', 'mouseup', 'keydown', 'keyup']
+   */
+  events?: WindowEventName[]
+  /**
+   * Initial value of the returned ref
+   *
+   * @default null
+   */
+  initial?: Initial
+}
+export type UseKeyModifierReturn<Initial> = ShallowRef<
+  Initial extends boolean ? boolean : boolean | null
+>
+export declare function useKeyModifier<Initial extends boolean | null>(
+  modifier: KeyModifier,
+  options?: UseModifierOptions<Initial>,
+): UseKeyModifierReturn<Initial>
+```