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

backend/routes/users.js

@@ -19,6 +19,7 @@
 
 const express = require('express');
 const bcrypt = require('bcryptjs');
+const crypto = require('crypto');
 const { query, getRow } = require('../db');
 const { authenticate, requireRole } = require('../middleware/auth');
 
@@ -115,10 +116,12 @@ router.post('/', authenticate, requireRole('owner','admin'), async (req, res) =>
   if (await getRow('SELECT id FROM users WHERE username = ?', [username])) return res.status(400).json({ error: '用户名已存在' });
   if (await getRow('SELECT id FROM users WHERE email = ?', [email])) return res.status(400).json({ error: '邮箱已被使用' });
   const hashed = bcrypt.hashSync(password, 10);
-  const r = await query('INSERT INTO users(username, password, email, game_name, game_uid, role, source, active, email_verified) VALUES (?,?,?,?,?,?,?,1,1)', [username, hashed, email, game_name, game_uid||'', role, source || '']);
+  // 游戏UID为内置参数: 管理员未指定时自动生成
+  const builtinUid = game_uid || ('U' + crypto.randomBytes(6).toString('hex').toUpperCase());
+  const r = await query('INSERT INTO users(username, password, email, game_name, game_uid, role, source, active, email_verified) VALUES (?,?,?,?,?,?,?,1,1)', [username, hashed, email, game_name, builtinUid, role, source || '']);
   try {
     await query('INSERT INTO user_identities(user_id, source, game_name, game_uid) VALUES (?,?,?,?)',
-      [r.insertId, source || '', game_name, game_uid || '']);
+      [r.insertId, source || '', game_name, builtinUid]);
   } catch {}
   await query("INSERT INTO audit_logs(user_id, username, action, entity_type, entity_id, details) VALUES (?,?,?,?,?,?)", [req.user.id, req.user.username, 'create_user', 'user', r.insertId, `创建用户 ${username}`]);
   res.status(201).json({ id: r.insertId, message: '创建成功' });