fix(account): 修复账户余额计算逻辑

- 移除实际扣减小于预扣减时的余额调整逻辑
- 删除最终扣减为0时预扣减加回余额的处理
- 简化账户余额更新流程，避免重复计算

src/main/java/com/kexue/skills/service/impl/AccountFrozenServiceImpl.java

@@ -234,16 +234,7 @@ public class AccountFrozenServiceImpl implements AccountFrozenService {
                 } else {
                     account.setBalance(balance.subtract(finalAmount));
                 }
-                
-                // 实际扣减小于预扣减，将剩余预扣减加回balance
-                if (finalAmount.compareTo(accountFrozen.getFrozenAmount()) < 0) {
-                    BigDecimal remainingFrozen = accountFrozen.getFrozenAmount().subtract(finalAmount);
-                    account.setBalance(account.getBalance().add(remainingFrozen));
-                }
             }
-        } else {
-            // 最终扣减为0，将预扣减全部加回balance
-            account.setBalance(balance.add(accountFrozen.getFrozenAmount()));
         }
 
         account.setUpdateTime(new Date());