feat: 品牌更名为 51短剧,替换新 logo

- 页面标题、登录、首页、header 文案改为「51短剧后台管理系统」
- public/icon.webp 与 src/assets/images/icon.webp 替换为新 logo
- prod_build.sh 部署路径同步改为 /server/51dj/webadmin/

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/views/main/components/header.vue

@@ -2,7 +2,7 @@
   <el-header>
     <div class="logo-text">
       <img :src="logoImg" class="logoImg" />
-      <span>黄果漫剧后台管理系统</span>
+      <span>51短剧后台管理系统</span>
     </div>
     <div class="header-btn">
       <el-select