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/ticket-detail.js

@@ -42,7 +42,7 @@ const TicketDetail = {
 <div class="detail-grid"><div>
   <div class="card"><div class="card-h"><span>基本信息</span><div>${U.badge(t.status,'status')} ${U.badge(t.type,'type')} ${U.badge(t.priority,'priority')}</div></div><div class="card-b">
     <div class="detail-row"><span class="lbl">标题</span><span class="val fb">${U.esc(t.title)}</span></div>
-    <div class="detail-row"><span class="lbl">提交者</span><span class="val">${U.esc(t.reporter_game_name)} (UID: ${U.esc(t.reporter_game_uid)})</span></div>
+    <div class="detail-row"><span class="lbl">提交者</span><span class="val">${U.esc(t.reporter_game_name)}</span></div>
     ${isRep?`<div class="detail-row"><span class="lbl">被举报人</span><span class="val">${U.esc(t.target_game_name||'?')} (UID: ${U.esc(t.target_game_uid||'?')})</span></div>
     <div class="detail-row"><span class="lbl">原因</span><span class="val">${U.esc(t.reason)}</span></div>`:''}
     ${isAppeal?`<div class="detail-row"><span class="lbl">申诉理由</span><span class="val">${U.esc(t.reason)}</span></div>`:''}