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/RegisterView.vue

@@ -61,14 +61,14 @@ async function handleRegister() {
         </div>
         <div class="mt-8 flex gap-4">
           <div class="border border-slate-200 bg-white px-4 py-3">
-            <div class="text-xs uppercase tracking-[0.2em] text-slate-500">Review</div>
-            <div class="mt-2 text-2xl font-bold text-slate-900">Queue</div>
-            <div class="mt-1 text-sm text-slate-500">上传后进入审核队列</div>
+            <div class="oc-stat-label">Review</div>
+            <div class="oc-stat-value">Queue</div>
+            <div class="oc-field-help">上传后进入审核队列</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">Profile</div>
-            <div class="mt-2 text-2xl font-bold text-slate-900">Journal</div>
-            <div class="mt-1 text-sm text-slate-500">自动生成个人天空日志</div>
+            <div class="oc-stat-label">Profile</div>
+            <div class="oc-stat-value">Journal</div>
+            <div class="oc-field-help">自动生成个人天空日志</div>
           </div>
         </div>
       </section>