refactor(styles): 建立统一的生产级样式体系 (#4)

## 变更内容

- 将全局样式拆分为设计令牌、基础规则和语义组件层
- 集中管理 Naive UI 主题配置
- 迁移页面容器、表单、信息面板和按钮等重复样式
- 增加样式体系文档与自动契约检查

## 验证

- `npm run check:styles`
- `npm run build`Reviewed-on: #4

src/views/auth/ForgotPasswordView.vue

@@ -85,14 +85,14 @@ onUnmounted(() => {
         </p>
         <div class="mt-8 grid gap-4 sm:grid-cols-2">
           <div class="border border-slate-200 bg-white px-4 py-3">
-            <div class="text-xs uppercase tracking-[0.2em] text-slate-500">Step 1</div>
+            <div class="oc-stat-label">Step 1</div>
             <div class="mt-2 text-lg font-bold text-slate-900">发送邮件</div>
-            <div class="mt-1 text-sm text-slate-500">使用注册邮箱请求重置链接</div>
+            <div class="oc-field-help">使用注册邮箱请求重置链接</div>
           </div>
           <div class="border border-slate-200 bg-white px-4 py-3">
-            <div class="text-xs uppercase tracking-[0.2em] text-slate-500">Step 2</div>
+            <div class="oc-stat-label">Step 2</div>
             <div class="mt-2 text-lg font-bold text-slate-900">设置新密码</div>
-            <div class="mt-1 text-sm text-slate-500">在专用页面完成新密码更新</div>
+            <div class="oc-field-help">在专用页面完成新密码更新</div>
           </div>
         </div>
       </section>