docs(vercel-react-best-practices): 添加 Vercel React 最佳实践规则文档

- 添加 sections 定义文件，包含性能优化各领域分类
- 添加规则模板文件，规范文档结构和标签定义
- 添加异步操作优化规则，包括防止瀑布流、并行化、延迟等待等
- 添加包大小优化规则，包括避免桶式导入、动态导入、预加载等
- 添加服务端性能优化规则，包括 API 路

.agents/skills/vercel-react-best-practices/rules/server-parallel-nested-fetching.md

@@ -0,0 +1,34 @@
+---
+title: Parallel Nested Data Fetching
+impact: CRITICAL
+impactDescription: eliminates server-side waterfalls
+tags: server, rsc, parallel-fetching, promise-chaining
+---
+
+## Parallel Nested Data Fetching
+
+When fetching nested data in parallel, chain dependent fetches within each item's promise so a slow item doesn't block the rest.
+
+**Incorrect (a single slow item blocks all nested fetches):**
+
+```tsx
+const chats = await Promise.all(
+  chatIds.map(id => getChat(id))
+)
+
+const chatAuthors = await Promise.all(
+  chats.map(chat => getUser(chat.author))
+)
+```
+
+If one `getChat(id)` out of 100 is extremely slow, the authors of the other 99 chats can't start loading even though their data is ready.
+
+**Correct (each item chains its own nested fetch):**
+
+```tsx
+const chatAuthors = await Promise.all(
+  chatIds.map(id => getChat(id).then(chat => getUser(chat.author)))
+)
+```
+
+Each item independently chains `getChat` → `getUser`, so a slow chat doesn't block author fetches for the others.