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%)

pkg/pagesarchive/entry.go

@@ -72,14 +72,14 @@ func copyLimited(dst io.Writer, src io.Reader, maxBytes int64) (int64, error) {
 		return written, err
 	}
 	if written > maxBytes {
-		return written, fmt.Errorf("pages file size out of bounds")
+		return written, errors.New("pages file size out of bounds")
 	}
 	return written, nil
 }
 
 func copyAndVerifySize(dst io.Writer, src io.Reader, declaredSize uint64, maxBytes int64) (int64, error) {
 	if declaredSize > uint64(math.MaxInt64) {
-		return 0, fmt.Errorf("pages file size out of bounds")
+		return 0, errors.New("pages file size out of bounds")
 	}
 	written, err := copyLimited(dst, src, maxBytes)
 	if err != nil {