fix(supply-api): 修复编译错误和测试问题

- 添加 ErrNotFound 和 ErrConcurrencyConflict 错误定义
- 修复 pgx.NullTime 替换为 *time.Time
- 修复 db.go 事务类型 (pgx.Tx vs pgxpool.Tx)
- 移除未使用的导入和变量
- 修复 NewSupplyAPI 调用参数
- 修复中间件链路 handler 类型问题
- 修复适配器类型引用 (storage.InMemoryAccountStore 等)
- 所有测试通过

Test: go test ./...

supply-api/internal/domain/invariants.go

@@ -191,9 +191,9 @@ func ValidateStateTransition(from, to AccountStatus) bool {
 // ValidatePackageStateTransition 验证套餐状态转换
 func ValidatePackageStateTransition(from, to PackageStatus) bool {
 	validTransitions := map[PackageStatus][]PackageStatus{
-		PackageStatusDraft:    {PackageStatusActive},
-		PackageStatusActive:   {PackageStatusPaused, PackageStatusSoldOut, PackageStatusExpired},
-		PackageStatusPaused:   {PackageStatusActive, PackageStatusExpired},
+		PackageStatusDraft:   {PackageStatusActive},
+		PackageStatusActive:  {PackageStatusPaused, PackageStatusSoldOut, PackageStatusExpired},
+		PackageStatusPaused:  {PackageStatusActive, PackageStatusExpired},
 		PackageStatusSoldOut: {}, // 只能由系统迁移
 		PackageStatusExpired: {}, // 不能直接恢复，需要通过克隆
 	}