前端: 修复浅色模式白字 + 主题优化

- 修 nav 激活态残留 text-zinc-50 导致浅色下白字白底
- @theme 令牌改实色字面量, 浅色用 [data-theme=light] 覆盖同一批 --color-*
- 新增 soft 令牌(accent/ok/warn/err, color-mix 运行时解析)替代烘焙的透明度修饰符,
  修复 badge 实色底、focus ring 实线等问题
- ThemeToggle 改三选下拉(浅色/深色/跟随系统), 系统自动为显式选项
- 浅色强调色调深保证 WCAG 对比度, 全量复查无残留硬编码颜色类

Co-Authored-By: Claude <noreply@anthropic.com>

web/src/views/console/DashboardView.vue

@@ -95,13 +95,13 @@ onMounted(load)
           <h2 class="text-sm font-semibold">最近请求</h2>
           <router-link to="/console/usage" class="text-xs text-accent hover:text-accent-strong">查看全部</router-link>
         </div>
-        <ul v-if="loading" class="divide-y divide-edge/70">
+        <ul v-if="loading" class="divide-y divide-edge">
           <li v-for="i in 4" :key="i" class="flex items-center justify-between py-2">
             <Skeleton height="0.75rem" width="40%" />
             <Skeleton height="0.75rem" width="30%" />
           </li>
         </ul>
-        <ul v-else class="divide-y divide-edge/70">
+        <ul v-else class="divide-y divide-edge">
           <li v-for="l in logs" :key="l.id" class="flex items-center justify-between py-2">
             <div class="min-w-0">
               <p class="truncate font-mono text-xs text-ink">{{ l.model }}</p>