chore(lint): unify formatting on golangci-lint fmt (gofumpt), uncap issue reporting, fix gofumpt drift

- make format 现在与 code-check 使用同一格式化器（golangci-lint fmt），消除 goimports -local 与 gofumpt 的格式拉锯
- .golangci.yml 关闭默认 50/3 截断，完整上报所有问题（只增强不弱化）
- 全库 gofumpt 规范化（203 files, 纯格式无行为变更）

backend/pkg/batchwriter/writer.go

@@ -242,7 +242,7 @@ func (w *Writer[T]) run() {
 	}
 }
 
-func (w *Writer[T]) shouldFlushOnInterval(batchLen int, batchStartedAt time.Time, now time.Time) bool {
+func (w *Writer[T]) shouldFlushOnInterval(batchLen int, batchStartedAt, now time.Time) bool {
 	if batchLen == 0 {
 		return false
 	}