feat: game UID fully internal + remove multi-identity copy

- game_uid is now an internal param: auto-generated server-side
  (U + 12 hex) on register/bind-identity/install/admin-create/external
  register; player-supplied game_uid ignored
- Removed all player-facing UID inputs: register page, install page,
  identity bind modal, ticket-create 'your UID' field
- Removed player-facing UID display: identity table column,
  ticket detail/tracking reporter UID
- Removed '同一账号可绑定网易端 + 皮肤站身份' / '可绑定多个来源身份' copy
- Kept target_game_uid (reported player) and admin panel UID management
- settings-page skin-site placeholder updated

public/js/pages/install.js

@@ -91,7 +91,6 @@ const InstallPage = {
           <div class="form-group"><label>邮箱 *</label><input type="email" id="ia-email" required></div></div>
           <div class="grid-2"><div class="form-group"><label>密码 *</label><input type="password" id="ia-password" required minlength="6"></div>
           <div class="form-group"><label>游戏名称</label><input id="ia-game" placeholder="Minecraft ID"></div></div>
-          <div class="form-group"><label>游戏UID</label><input id="ia-uid" placeholder="游戏唯一ID"></div>
           <div id="ia-err" class="alert alert-e hidden"></div>
           <div id="ia-warn" class="alert alert-i"><strong>注意：</strong>安装完成后需要重启服务器才能加载业务路由。请记好账号密码。</div>
           <button type="submit" class="btn btn-p btn-lg w-full"><i class="fas fa-check"></i> 完成安装</button>
@@ -114,7 +113,6 @@ const InstallPage = {
           admin_password: document.getElementById('ia-password').value,
           admin_email: document.getElementById('ia-email').value,
           admin_game_name: document.getElementById('ia-game').value,
-          admin_game_uid: document.getElementById('ia-uid').value,
         });
         document.getElementById('install-admin').innerHTML = '<div class="alert alert-s"><h3><i class="fas fa-check-circle"></i> 安装成功！</h3><p>系统已就绪，正在刷新并跳转登录...</p></div>';
         setTimeout(() => location.reload(), 1500);