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/LeagueAccordionItem.vue

@@ -1,8 +1,8 @@
 <script setup lang="ts">
 import { computed } from 'vue';
 import MatchBetCard from './MatchBetCard.vue';
-import saishiImg from '../assets/images/saishi.png';
-import cardBg from '../assets/images/card-bg.png';
+import saishiImg from '../assets/images/saishi.webp';
+import cardBg from '../assets/images/card-bg.webp';
 
 const matchCardBg = `url(${cardBg})`;