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/admin/status/routers.go

@@ -14,6 +14,7 @@ import (
 	"os"
 	"os/exec"
 	"runtime"
+	"strconv"
 	"time"
 
 	"github.com/Rain-kl/Wavelet/internal/infra/config"
@@ -309,7 +310,7 @@ func exportSQLite(c *gin.Context) {
 
 	c.Header("Content-Disposition", `attachment; filename="openflare.db"`)
 	c.Header("Content-Type", "application/octet-stream")
-	c.Header("Content-Length", fmt.Sprintf("%d", fi.Size()))
+	c.Header("Content-Length", strconv.FormatInt(fi.Size(), 10))
 	c.Status(http.StatusOK)
 	http.ServeContent(c.Writer, c.Request, "openflare.db", fi.ModTime(), f)
 }
@@ -328,7 +329,7 @@ func exportPostgres(c *gin.Context) {
 	args := []string{
 		"--no-password",
 		"-h", dbCfg.Host,
-		"-p", fmt.Sprintf("%d", dbCfg.Port),
+		"-p", strconv.Itoa(dbCfg.Port),
 		"-U", dbCfg.Username,
 		dbCfg.Database,
 	}