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/register.js

@@ -49,8 +49,6 @@ const RegisterPage = {
             <div class="form-group"><label id="rs-label1">游戏名称</label><input id="rgn" required placeholder="Minecraft ID"></div>
           </div>
 
-          <div class="form-group" id="uid-group" style="display:none"><label id="rs-label2">UID(可选)</label><input id="rgu" placeholder="选填"></div>
-
           ${this.captcha ? `
           <div class="form-group"><label>人机验证</label>
             <div style="display:flex;align-items:center;gap:10px">
@@ -85,10 +83,6 @@ const RegisterPage = {
   toggleSource() {
     const src = document.getElementById('rs').value;
     document.getElementById('rs-label1').textContent = '游戏名称';
-    const isSkin = src === 'skin';
-    document.getElementById('rs-label2').textContent = isSkin ? '皮肤站UUID(可选)' : 'UID(可选)';
-    document.getElementById('uid-group').style.display = isSkin ? 'none' : '';
-    document.getElementById('rgu').required = false;
   },
 
   async refreshCaptcha() {
@@ -124,7 +118,7 @@ const RegisterPage = {
         await Auth.register({
           username: document.getElementById('ru').value.trim(), password: document.getElementById('rp').value,
           email: document.getElementById('re').value.trim(), game_name: document.getElementById('rgn').value.trim(),
-          game_uid: document.getElementById('rgu').value.trim(), source: document.getElementById('rs').value,
+          source: document.getElementById('rs').value,
           captcha_id: document.getElementById('captcha-id')?.value,
           captcha_answer: document.getElementById('captcha-a')?.value.trim(),
           code_id: this.codeId, code: document.getElementById('vf-code').value.trim(),