modernize 37→5（-32）：interface{}→any、内置 max/min、slices/maps 辅助、strings.Cut/SplitSeq、strings.Builder（修复 mail.go O(n²) 拼接）。逐 hunk 核对语义等价；omitzero 冲突修复被自动跳过（wire 格式不变）；手动清 4 处遗留 sort import + 2 处 QF1012。

Result: {"status":"keep","total_issues":74,"golint_canonicalheader":8,"golint_errname":1,"golint_errorlint":12,"golint_forcetypeassert":3,"golint_gosec":0,"golint_intrange":3,"golint_modernize":5,"golint_nilnil":3,"golint_perfsprint":18,"golint_prealloc":3,"golint_recvcheck":7,"golint_usestdlibvars":3,"golint_wastedassign":7,"golint_total":73,"eslint_problems":1,"eslint_errors":0,"eslint_warnings":1,"tsc_errors":0,"measure_s":38}

pkg/geoip/country_centroid.go

@@ -194,7 +194,7 @@ func CountryCentroidByName(name string) (lat float64, lon float64, ok bool) {
 		return v.lat, v.lon, true
 	}
 	// Try comma-separated parts (city / region / country / ISO).
-	for _, part := range strings.Split(name, ",") {
+	for part := range strings.SplitSeq(name, ",") {
 		part = strings.TrimSpace(part)
 		if part == "" {
 			continue