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/createProjection.md

@@ -0,0 +1,31 @@
+---
+category: '@Math'
+related: useProjection, createGenericProjection
+---
+
+# createProjection
+
+Reactive numeric projection from one domain to another.
+
+## Usage
+
+```ts
+import { createProjection } from '@vueuse/math'
+
+const useProjector = createProjection([0, 10], [0, 100])
+const input = ref(0)
+const projected = useProjector(input) // projected.value === 0
+
+input.value = 5 // projected.value === 50
+input.value = 10 // projected.value === 100
+```
+
+## Type Declarations
+
+```ts
+export declare function createProjection(
+  fromDomain: MaybeRefOrGetter<readonly [number, number]>,
+  toDomain: MaybeRefOrGetter<readonly [number, number]>,
+  projector?: ProjectorFunction<number, number>,
+): UseProjection<number, number>
+```