Resolve host IPs through DNS, add purge, French date format by default

- Reverse DNS (cached PTR lookups): IP hosts are stored with their name
  in 'host' and the IP in 'host_ip'; older IP-only logs are resolved on
  display and the host filter shows 'name (IP)'. RDNS / DNS_SERVER env.
- Settings > Danger zone: delete all logs (type PURGE to confirm) through
  VictoriaLogs /delete/run_task; -delete.enable added to docker-compose.
  ALLOW_PURGE env to disable it.
- Remove the custom YYYY-MM-DD - HH:MM:SS:mmm format; default is now the
  usual French display DD/MM/YYYY HH:MM:SS.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.go

@@ -15,6 +15,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"strconv"
+	"strings"
 	"syscall"
 	"time"
 	_ "time/tzdata" // embedded time zones: TZ works without a system package
@@ -30,6 +31,9 @@ type config struct {
 	dataDir    string
 	authUser   string
 	authPass   string
+	rdns       bool
+	dnsServer  string
+	allowPurge bool
 	batchSize  int
 	queueSize  int
 	flushEvery time.Duration
@@ -49,6 +53,16 @@ func getenvInt(key string, def int) int {
 	return def
 }
 
+func getenvBool(key string, def bool) bool {
+	switch strings.ToLower(os.Getenv(key)) {
+	case "1", "true", "yes", "on":
+		return true
+	case "0", "false", "no", "off":
+		return false
+	}
+	return def
+}
+
 func main() {
 	cfg := config{
 		syslogAddr: getenv("SYSLOG_ADDR", ":5514"),
@@ -57,6 +71,9 @@ func main() {
 		dataDir:    getenv("DATA_DIR", "/data"),
 		authUser:   os.Getenv("AUTH_USER"),
 		authPass:   os.Getenv("AUTH_PASS"),
+		rdns:       getenvBool("RDNS", true),
+		dnsServer:  os.Getenv("DNS_SERVER"),
+		allowPurge: getenvBool("ALLOW_PURGE", true),
 		batchSize:  getenvInt("BATCH_SIZE", 1000),
 		queueSize:  getenvInt("QUEUE_SIZE", 100000),
 		flushEvery: time.Duration(getenvInt("FLUSH_MS", 1000)) * time.Millisecond,
@@ -78,7 +95,13 @@ func main() {
 	}()
 
 	hub := NewHub()
+	rdns := NewReverseDNS(cfg.rdns, cfg.dnsServer)
 	sink := func(e *Entry) {
+		// Host sent as an IP (or no host in the header): replace it with its DNS name.
+		// A new IP waits at most 300 ms; slower lookups finish in the background.
+		if name := rdns.Lookup(e.Host, 300*time.Millisecond); name != "" {
+			e.HostIP, e.Host = e.Host, name
+		}
 		store.Enqueue(e)
 		hub.Publish(e)
 	}
@@ -91,7 +114,7 @@ func main() {
 		log.Fatal(err)
 	}
 	mux := http.NewServeMux()
-	api := &API{store: store, hub: hub, tags: tags}
+	api := &API{store: store, hub: hub, tags: tags, rdns: rdns, allowPurge: cfg.allowPurge}
 	api.Routes(mux)
 	mux.Handle("GET /", http.FileServer(http.FS(static)))