fix(middleware): 管理员JWT增加TokenVersion校验

管理员改密后旧JWT会被拒绝，并补充单元测试覆盖。

backend/internal/server/api_contract_test.go

@@ -598,7 +598,7 @@ func newContractDeps(t *testing.T) *contractDeps {
 	usageRepo := newStubUsageLogRepo()
 	usageService := service.NewUsageService(usageRepo, userRepo, nil, nil)
 
-	subscriptionService := service.NewSubscriptionService(groupRepo, userSubRepo, nil)
+	subscriptionService := service.NewSubscriptionService(groupRepo, userSubRepo, nil, cfg)
 	subscriptionHandler := handler.NewSubscriptionHandler(subscriptionService)
 
 	redeemService := service.NewRedeemService(redeemRepo, userRepo, subscriptionService, nil, nil, nil, nil)