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/pinia/references/features-composing-stores.md

@@ -0,0 +1,134 @@
+---
+name: composing-stores
+description: Store-to-store communication and avoiding circular dependencies
+---
+
+# Composing Stores
+
+Stores can use each other for shared state and logic.
+
+## Rule: Avoid Circular Dependencies
+
+Two stores cannot directly read each other's state during setup:
+
+```ts
+// ❌ Infinite loop
+const useX = defineStore('x', () => {
+  const y = useY()
+  y.name // Don't read here!
+  return { name: ref('X') }
+})
+
+const useY = defineStore('y', () => {
+  const x = useX()
+  x.name // Don't read here!
+  return { name: ref('Y') }
+})
+```
+
+**Solution:** Read in getters, computed, or actions:
+
+```ts
+const useX = defineStore('x', () => {
+  const y = useY()
+
+  // ✅ Read in computed/actions
+  function doSomething() {
+    const yName = y.name
+  }
+
+  return { name: ref('X'), doSomething }
+})
+```
+
+## Setup Stores: Use Store at Top
+
+```ts
+import { defineStore } from 'pinia'
+import { useUserStore } from './user'
+
+export const useCartStore = defineStore('cart', () => {
+  const user = useUserStore()
+  const list = ref([])
+
+  const summary = computed(() => {
+    return `Hi ${user.name}, you have ${list.value.length} items`
+  })
+
+  function purchase() {
+    return apiPurchase(user.id, list.value)
+  }
+
+  return { list, summary, purchase }
+})
+```
+
+## Shared Getters
+
+Call `useStore()` inside a getter:
+
+```ts
+import { useUserStore } from './user'
+
+export const useCartStore = defineStore('cart', {
+  getters: {
+    summary(state) {
+      const user = useUserStore()
+      return `Hi ${user.name}, you have ${state.list.length} items`
+    },
+  },
+})
+```
+
+## Shared Actions
+
+Call `useStore()` inside an action:
+
+```ts
+import { useUserStore } from './user'
+import { apiOrderCart } from './api'
+
+export const useCartStore = defineStore('cart', {
+  actions: {
+    async orderCart() {
+      const user = useUserStore()
+
+      try {
+        await apiOrderCart(user.token, this.items)
+        this.emptyCart()
+      } catch (err) {
+        displayError(err)
+      }
+    },
+  },
+})
+```
+
+## SSR: Call Stores Before Await
+
+In async actions, call all stores before any `await`:
+
+```ts
+actions: {
+  async orderCart() {
+    // ✅ All useStore() calls before await
+    const user = useUserStore()
+    const analytics = useAnalyticsStore()
+
+    try {
+      await apiOrderCart(user.token, this.items)
+      // ❌ Don't call useStore() after await (SSR issue)
+      // const otherStore = useOtherStore()
+    } catch (err) {
+      displayError(err)
+    }
+  },
+}
+```
+
+This ensures the correct Pinia instance is used during SSR.
+
+<!--
+Source references:
+- https://pinia.vuejs.org/cookbook/composing-stores.html
+-->