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)

service/geo.go

@@ -36,6 +36,9 @@ func NewGeo(ctx context.Context, cityPath string, asnPath string) (*Geo, error)
 }
 
 func (g *Geo) LookUpCity(ip net.IP) *models.GeoRecord {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
 	record, err := g.db.LookupCity(ip)
 	if err != nil {
 		log.Print(err)
@@ -47,6 +50,9 @@ func (g *Geo) LookUpCity(ip net.IP) *models.GeoRecord {
 }
 
 func (g *Geo) LookUpASN(ip net.IP) *models.ASNRecord {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
 	record, err := g.db.LookupASN(ip)
 	if err != nil {
 		log.Print(err)
@@ -59,7 +65,13 @@ func (g *Geo) LookUpASN(ip net.IP) *models.ASNRecord {
 
 func (g *Geo) Shutdown() {
 	g.cancel()
-	g.db.CloseDBs()
+
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if err := g.db.CloseDBs(); err != nil {
+		log.Printf("Error closing geo databases: %s", err)
+	}
 }
 
 func (g *Geo) Reload() {
@@ -71,6 +83,9 @@ func (g *Geo) Reload() {
 	g.mu.Lock()
 	defer g.mu.Unlock()
 
-	g.db.Reload()
+	if err := g.db.Reload(); err != nil {
+		log.Printf("Geo database reload failed: %s", err)
+		return
+	}
 	log.Print("Geo database reloaded")
 }