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/rerender-derived-state-no-effect.md

@@ -0,0 +1,40 @@
+---
+title: Calculate Derived State During Rendering
+impact: MEDIUM
+impactDescription: avoids redundant renders and state drift
+tags: rerender, derived-state, useEffect, state
+---
+
+## Calculate Derived State During Rendering
+
+If a value can be computed from current props/state, do not store it in state or update it in an effect. Derive it during render to avoid extra renders and state drift. Do not set state in effects solely in response to prop changes; prefer derived values or keyed resets instead.
+
+**Incorrect (redundant state and effect):**
+
+```tsx
+function Form() {
+  const [firstName, setFirstName] = useState('First')
+  const [lastName, setLastName] = useState('Last')
+  const [fullName, setFullName] = useState('')
+
+  useEffect(() => {
+    setFullName(firstName + ' ' + lastName)
+  }, [firstName, lastName])
+
+  return <p>{fullName}</p>
+}
+```
+
+**Correct (derive during render):**
+
+```tsx
+function Form() {
+  const [firstName, setFirstName] = useState('First')
+  const [lastName, setLastName] = useState('Last')
+  const fullName = firstName + ' ' + lastName
+
+  return <p>{fullName}</p>
+}
+```
+
+References: [You Might Not Need an Effect](https://react.dev/learn/you-might-not-need-an-effect)