后端与全仓代码质量清理（golangci 扩展集 · 测试质量 · 并发安全 · 文档同步）

代码质量全量清理，零行为变化：golangci 扩展集 13 类 linter（gosec/modernize/perfsprint/canonicalheader/usestdlibvars/wastedassign/intrange/errorlint/forcetypeassert/recvcheck/exhaustive/unparam）全量修复，测试代码质量（testifylint/thelper/usetesting）25→0，frpc 进程生命周期真 bug（进程组击杀）、全仓 go test -race 6 类数据竞争（含 1 个生产竞争）、SPDX license 头补齐 131 文件、前端测试套件 next-intl 迁移后 44 失败→全绿、过期 swagger 文档重新生成、pnpm-workspace 构建审批。

Experiments: #2-#17, #18, #20, #21, #23
Metric: total_issues 108 → 8 (-92.6%)

internal/apps/openflare/flared/logics.go

@@ -28,7 +28,7 @@ const (
 // Heartbeat processes an OpenFlared heartbeat and returns runtime settings.
 func Heartbeat(ctx context.Context, node *model.OpenFlareNode, payload HeartbeatPayload) (*HeartbeatResponse, error) {
 	if node == nil {
-		return nil, fmt.Errorf("tunnel client node is nil")
+		return nil, errors.New("tunnel client node is nil")
 	}
 	if node.NodeType != "tunnel_client" {
 		return nil, fmt.Errorf("node %s is not a tunnel_client", node.NodeID)
@@ -95,7 +95,7 @@ func Heartbeat(ctx context.Context, node *model.OpenFlareNode, payload Heartbeat
 // GetTunnelConfig builds the full tunnel routing config for an OpenFlared client.
 func GetTunnelConfig(ctx context.Context, node *model.OpenFlareNode) (*TunnelConfigResponse, error) {
 	if node == nil {
-		return nil, fmt.Errorf("node is nil")
+		return nil, errors.New("node is nil")
 	}
 
 	activeVersion, err := getActiveConfigMeta(ctx)