fix: auto-fix code issues (cron)

- 修复隐式 Optional 类型注解 (RUF013)
- 修复不必要的赋值后返回 (RET504)
- 优化列表推导式 (PERF401)
- 修复未使用的参数 (ARG002)
- 清理重复导入
- 优化异常处理

backend/test_phase8_task5.py

@@ -525,7 +525,8 @@ class TestGrowthManager:
 
         try:
             referral = self.manager.generate_referral_code(
-                program_id=program_id, referrer_id="referrer_user_001",
+                program_id=program_id,
+                referrer_id="referrer_user_001",
             )
 
             if referral:
@@ -551,7 +552,8 @@ class TestGrowthManager:
 
         try:
             success = self.manager.apply_referral_code(
-                referral_code=referral_code, referee_id="new_user_001",
+                referral_code=referral_code,
+                referee_id="new_user_001",
             )
 
             if success:
@@ -618,7 +620,9 @@ class TestGrowthManager:
 
         try:
             incentives = self.manager.check_team_incentive_eligibility(
-                tenant_id=self.test_tenant_id, current_tier="free", team_size=5,
+                tenant_id=self.test_tenant_id,
+                current_tier="free",
+                team_size=5,
             )
 
             self.log(f"找到 {len(incentives)} 个符合条件的激励")