Fix data races, nil-record panics, scanner SSRF, log date layout, shutdown timeouts, and enable stricter linters (#54)

High (behavioral bugs):
- service.Geo: add RLock on lookups, handle Reload error, keep old DBs on failure
- models.GeoDB.Reload: open new DBs before closing old ones (no reader gap)
- router: guard nil geo records (404 instead of 500) in geo.go, generic.go, dns.go
- router/port_scanner: reject undetermined client IPs (nil->localhost dial)
- internal/httputils: fix access log date layout (02/Jan/2006, not literal Nov)
- server/quic: log.Printf instead of log.Fatal in request handler

Medium:
- server/*: 10s shutdown timeout; SIGTERM drains servers before closing geo DBs
- httputils: Clone() request headers instead of mutating the live map; strings.Builder
- setting/app: handle all os.Stat errors; fix "truster" typos; use errors.New;
  remove dead Token field
- cmd: errors.Is for sentinel checks; os.Stderr; log.Fatal instead of panic;
  pass http.Handler by value (not pointer-to-interface)
- resolver: validate config at startup (pre-parse RRs, validate IPs); check WriteMsg
  errors; Setup returns error

Low:
- .golangci.yaml: enable errcheck, govet, errorlint; fix all resulting findings
- server/tls: explicit TLSConfig{MinVersion: tls.VersionTLS12}
- router/dns: label-exact vhost suffix check, strip port; template.Must
- models: errors.Join instead of %s on []error
- service/geo_test: race-regression test (concurrent lookups during Reload)
- README: Go >= 1.25; fix latent test bug (store.Add->Set in dns_test.go)

router/dns.go

@@ -29,12 +29,13 @@ type dnsData struct {
 // Implement a proper vhost manager instead of using a middleware
 func GetDNSDiscoveryHandler(store *cache.Cache, domain string, redirectPort string) gin.HandlerFunc {
 	return func(ctx *gin.Context) {
-		if !strings.HasSuffix(ctx.Request.Host, domain) {
+		host := hostWithoutPort(ctx.Request.Host)
+		if host != domain && !strings.HasSuffix(host, "."+domain) {
 			ctx.Next()
 			return
 		}
 
-		if ctx.Request.Host == domain && ctx.Request.URL.Path == "/" {
+		if host == domain && ctx.Request.URL.Path == "/" {
 			ctx.Redirect(http.StatusFound, fmt.Sprintf("http://%s.%s%s", uuid.New().String(), domain, redirectPort))
 			ctx.Abort()
 			return
@@ -45,6 +46,13 @@ func GetDNSDiscoveryHandler(store *cache.Cache, domain string, redirectPort stri
 	}
 }
 
+func hostWithoutPort(host string) string {
+	if h, _, err := net.SplitHostPort(host); err == nil {
+		return h
+	}
+	return host
+}
+
 func handleDNS(ctx *gin.Context, store *cache.Cache) {
 	d := strings.Split(ctx.Request.Host, ".")[0]
 	if !validator.IsValid(d) {
@@ -72,12 +80,11 @@ func handleDNS(ctx *gin.Context, store *cache.Cache) {
 
 	geoResp := dnsGeoData{}
 	if geoSvc != nil {
-		cityRecord := geoSvc.LookUpCity(ip)
-		asnRecord := geoSvc.LookUpASN(ip)
-
-		geoResp = dnsGeoData{
-			Country:         cityRecord.Country.Names["en"],
-			AsnOrganization: asnRecord.AutonomousSystemOrganization,
+		if cityRecord := geoSvc.LookUpCity(ip); cityRecord != nil {
+			geoResp.Country = cityRecord.Country.Names["en"]
+		}
+		if asnRecord := geoSvc.LookUpASN(ip); asnRecord != nil {
+			geoResp.AsnOrganization = asnRecord.AutonomousSystemOrganization
 		}
 	}