perf(assets): Player/Admin 静态图改用 WebP，vs 保留 PNG

Player 端 banner/bg/card/h5bg 等改为 webp 并移除旧 png；Admin 登录背景改 webp；vs 对阵图仍用 png。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/player/src/components/BannerCarousel.vue

@@ -4,7 +4,7 @@ import { useRouter } from 'vue-router';
 import { useI18n } from 'vue-i18n';
 
 const { t } = useI18n();
-import defaultBannerImg from '../assets/images/banner.png';
+import defaultBannerImg from '../assets/images/banner.webp';
 
 export interface BannerItem {
   id?: string;