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/edge/updater/service.go

@@ -1,3 +1,6 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
 // Package updater provides capabilities to check for, download, and apply updates.
 package updater
 
@@ -6,6 +9,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -285,7 +289,7 @@ func (s *Service) downloadChecksum(ctx context.Context, url string, assetName st
 
 func parseSHA256Checksum(content string, assetName string) (string, error) {
 	assetName = strings.TrimSpace(assetName)
-	for _, line := range strings.Split(content, "\n") {
+	for line := range strings.SplitSeq(content, "\n") {
 		line = strings.TrimSpace(line)
 		if line == "" || strings.HasPrefix(line, "#") {
 			continue
@@ -295,7 +299,7 @@ func parseSHA256Checksum(content string, assetName string) (string, error) {
 		}
 	}
 	if assetName == "" {
-		return "", fmt.Errorf("checksum asset does not contain a valid sha256 digest")
+		return "", errors.New("checksum asset does not contain a valid sha256 digest")
 	}
 	return "", fmt.Errorf("checksum asset does not contain a sha256 digest for %q", assetName)
 }
@@ -340,7 +344,7 @@ func isSHA256Hex(value string) bool {
 func (s *Service) downloadAndRestart(ctx context.Context, url string, expectedChecksum string, targetPath string) error {
 	expectedChecksum = strings.ToLower(strings.TrimSpace(expectedChecksum))
 	if !isSHA256Hex(expectedChecksum) {
-		return fmt.Errorf("invalid expected sha256 checksum")
+		return errors.New("invalid expected sha256 checksum")
 	}
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {