fix: prevent username/email enumeration via registration error messages

backend/routes/external.js

@@ -24,8 +24,8 @@ router.post('/auth/register', async (req, res) => {
     const { username, password, email, game_name, game_uid } = req.body;
     if (!username || !password || !email || !game_name || !game_uid) return res.status(400).json({ error: '所有字段必填' });
     if (password.length < 6) return res.status(400).json({ error: '密码至少6位' });
-    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: '邮箱已注册' });
+    if (await getRow('SELECT id FROM users WHERE username = ?', [username])) return res.status(400).json({ error: '注册失败，请检查输入信息' });
+    if (await getRow('SELECT id FROM users WHERE email = ?', [email])) return res.status(400).json({ error: '注册失败，请检查输入信息' });
 
     const hashed = bcrypt.hashSync(password, 10);
     const verifyToken = uuid();