fix: 修复代码审核发现的10个问题（P0安全+P1数据一致性+P2性能优化）

P0: OpenAI SSE 错误消息 JSON 注入 — 使用 json.Marshal 替代 fmt.Sprintf
P1: subscription 续期包裹 Ent 事务确保原子性
P1: CSP nonce 生成处理 crypto/rand 错误，失败降级为 unsafe-inline
P1: singleflight 透传数据库真实错误，不再吞没为 not found
P1: GetUserSubscriptionsWithProgress 提取 calculateProgress 消除 N+1
P2: billing_cache/gateway_helper 迁移到 math/rand/v2 消除全局锁争用
P2: generateRandomID 降级分支增加原子计数器防碰撞
P2: CORS 非白名单 origin 不再设置 Allow-Headers/Methods/Max-Age
P2: Turnstile 验证移除 VerifyCode 空值跳过条件防绕过
P2: Redis Cluster Lua 脚本空 KEYS 添加兼容性警告注释

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/cmd/server/wire_gen.go

@@ -66,7 +66,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	promoService := service.NewPromoService(promoCodeRepository, userRepository, billingCacheService, client, apiKeyAuthCacheInvalidator)
 	authService := service.NewAuthService(userRepository, redeemCodeRepository, refreshTokenCache, configConfig, settingService, emailService, turnstileService, emailQueueService, promoService)
 	userService := service.NewUserService(userRepository, apiKeyAuthCacheInvalidator, billingCache)
-	subscriptionService := service.NewSubscriptionService(groupRepository, userSubscriptionRepository, billingCacheService, configConfig)
+	subscriptionService := service.NewSubscriptionService(groupRepository, userSubscriptionRepository, billingCacheService, client, configConfig)
 	redeemCache := repository.NewRedeemCache(redisClient)
 	redeemService := service.NewRedeemService(redeemCodeRepository, userRepository, subscriptionService, redeemCache, billingCacheService, client, apiKeyAuthCacheInvalidator)
 	secretEncryptor, err := repository.NewAESEncryptor(configConfig)