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/httppool/httppool_test.go

@@ -52,7 +52,7 @@ func TestNewTransportUsesConfiguredDirectDialer(t *testing.T) {
 	dialer := &net.Dialer{}
 	transport := NewTransport(TransportOptions{
 		Proxy: nil,
-		DialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
+		DialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
 			dialedAddress = address
 			return dialer.DialContext(ctx, network, server.Listener.Addr().String())
 		},