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/useRTDB.md

@@ -0,0 +1,83 @@
+---
+category: '@Firebase'
+---
+
+# useRTDB
+
+Reactive [Firebase Realtime Database](https://firebase.google.com/docs/database) binding. Making it straightforward to **always keep your local data in sync** with remotes databases.
+
+## Usage
+
+```ts
+import { useRTDB } from '@vueuse/firebase/useRTDB'
+import { initializeApp } from 'firebase/app'
+import { getDatabase } from 'firebase/database'
+
+const app = initializeApp({ /* config */ })
+const db = getDatabase(app)
+
+// in setup()
+const todos = useRTDB(db.ref('todos'))
+```
+
+## Options
+
+| Option         | Type                   | Default         | Description                                               |
+| -------------- | ---------------------- | --------------- | --------------------------------------------------------- |
+| `autoDispose`  | `boolean`              | `true`          | Automatically unsubscribe when the component is unmounted |
+| `errorHandler` | `(err: Error) => void` | `console.error` | Custom error handler for database errors                  |
+
+## Return Value
+
+Returns a `Ref<T | undefined>` that is automatically updated when the database value changes.
+
+## Reusing Database References
+
+You can reuse the db reference by passing `autoDispose: false`
+
+```ts
+const todos = useRTDB(db.ref('todos'), { autoDispose: false })
+```
+
+or use `createGlobalState` from the core package
+
+```ts twoslash include store
+// @filename: store.ts
+// ---cut---
+// store.ts
+import { createGlobalState } from '@vueuse/core'
+import { useRTDB } from '@vueuse/firebase/useRTDB'
+
+export const useTodos = createGlobalState(
+  () => useRTDB(db.ref('todos')),
+)
+```
+
+```vue
+<!-- app.vue -->
+<script setup lang="ts">
+// @include: store
+// ---cut---
+import { useTodos } from './store'
+
+const todos = useTodos()
+</script>
+```
+
+## Type Declarations
+
+```ts
+export interface UseRTDBOptions {
+  errorHandler?: (err: Error) => void
+  autoDispose?: boolean
+}
+/**
+ * Reactive Firebase Realtime Database binding.
+ *
+ * @see https://vueuse.org/useRTDB
+ */
+export declare function useRTDB<T = any>(
+  docRef: DatabaseReference,
+  options?: UseRTDBOptions,
+): Ref<T | undefined, T | undefined>
+```