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/cap/cap.go

@@ -215,7 +215,7 @@ func VerifyChallengeSolutions(token string, solutions []int, secret []byte, expe
 	}
 
 	tokenFnv := fnv1a(token)
-	for i := 0; i < payload.Count; i++ {
+	for i := range payload.Count {
 		idxStr := strconv.Itoa(i + 1)
 		saltSeed := fnv1aResume(tokenFnv, idxStr)
 		targetSeed := fnv1aResume(saltSeed, "d")
@@ -238,14 +238,14 @@ func VerifyChallengeSolutions(token string, solutions []int, secret []byte, expe
 func Solve(token string, count, size, difficulty int) []int {
 	solutions := make([]int, count)
 	tokenFnv := fnv1a(token)
-	for i := 0; i < count; i++ {
+	for i := range count {
 		idxStr := strconv.Itoa(i + 1)
 		saltSeed := fnv1aResume(tokenFnv, idxStr)
 		targetSeed := fnv1aResume(saltSeed, "d")
 		salt := prngFromHash(saltSeed, size)
 		target := prngFromHash(targetSeed, difficulty)
 
-		for nonce := 0; nonce < 1000000; nonce++ {
+		for nonce := range 1000000 {
 			hashInput := salt + strconv.Itoa(nonce)
 			hashBytes := sha256.Sum256([]byte(hashInput))
 			hashHex := hex.EncodeToString(hashBytes[:])