style(frontend): 全局样式改为 klp-ui 浅色红主题

- variables.scss 整盘重配色：浅灰背景/白卡片、#C03639 红主色、element 标准状态色与字体栈
- global.scss element-ui 覆写由深色改为浅色+红主色，卡片加轻投影
- Material/Message 视图内硬编码深色数据面板改为浅色

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/views/Message.vue

@@ -153,7 +153,7 @@ export default {
 @import '@/assets/styles/variables';
 .action-link { color: $sms-highlight; cursor: pointer; font-size: 12px; &:hover { text-decoration: underline; } }
 .raw-box {
-  background: #0a0f18; color: #d4d4d4;
+  background: $bg-panel; color: $text-primary;
   padding: 12px; border-radius: 4px; border: 1px solid $border;
   font-size: 11px; font-family: $font-mono;
   max-height: 180px; overflow-y: auto;