feat(dashboard): HAProxy Listener-Stats + i18n-Relativzeit

- haproxy_stats.go: FRONTEND-Rows aus show-stat CSV auslesen und als
  frontends[] zurückgeben (Name, Sessions, MaxSess, Bytes, ReqTot/Rate)
- Dashboard: Listener-Sektion über Backend-Liste; query jetzt unified
  haproxyStats mit backends/frontends alias für Abwärtskompatibilität
- common.relTime.*-Keys (en+de) eingeführt; relativeTime/relativeFromIso
  in Dashboard + relTime in WireGuard Servers/Clients auf t-Parameter
  umgestellt statt hardcodierter Strings
- CertExpiry in Cluster-Seite nutzt jetzt certDaysRemaining/certExpiredDaysAgo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/handlers/haproxy_stats.go

@@ -44,18 +44,31 @@ type backendStat struct {
 	Health   string `json:"health,omitempty"` // check_status (e.g. L7OK)
 }
 
+// frontendStat holds per-listener traffic counters from HAProxy's
+// show-stat CSV. Gives the operator a global view of how much HTTP(S)
+// traffic is flowing through the gateway.
+type frontendStat struct {
+	Name     string `json:"name"`      // pxname (e.g. "https_in", "http_in")
+	Sessions int64  `json:"sessions"`  // current sessions (scur)
+	MaxSess  int64  `json:"max_sess"`  // maximum concurrent sessions since start (smax)
+	BIn      int64  `json:"bytes_in"`
+	BOut     int64  `json:"bytes_out"`
+	ReqTot   int64  `json:"req_tot"`  // total requests since start
+	ReqRate  int64  `json:"req_rate"` // requests/s last second
+}
+
 func (h *HAProxyStatsHandler) Stats(c *gin.Context) {
 	conn, err := net.DialTimeout("unix", haproxyAdminSock, 2*time.Second)
 	if err != nil {
 		// Socket nicht erreichbar (haproxy down oder no perm) →
 		// leere Liste statt 500 damit das Dashboard nicht rot wird.
-		response.OK(c, gin.H{"backends": []backendStat{}, "error": err.Error()})
+		response.OK(c, gin.H{"backends": []backendStat{}, "frontends": []frontendStat{}, "error": err.Error()})
 		return
 	}
 	defer conn.Close()
 	_ = conn.SetDeadline(time.Now().Add(3 * time.Second))
 	if _, err := conn.Write([]byte("show stat\n")); err != nil {
-		response.OK(c, gin.H{"backends": []backendStat{}, "error": err.Error()})
+		response.OK(c, gin.H{"backends": []backendStat{}, "frontends": []frontendStat{}, "error": err.Error()})
 		return
 	}
 
@@ -63,7 +76,8 @@ func (h *HAProxyStatsHandler) Stats(c *gin.Context) {
 	// "# pxname,svname,..." — die nutzen wir um Spalten-Indizes
 	// zu finden, weil das Format zwischen Versionen wechseln kann.
 	colIdx := map[string]int{}
-	out := []backendStat{}
+	backends := []backendStat{}
+	frontends := []frontendStat{}
 
 	scanner := bufio.NewScanner(conn)
 	scanner.Buffer(make([]byte, 64*1024), 1024*1024)
@@ -81,18 +95,30 @@ func (h *HAProxyStatsHandler) Stats(c *gin.Context) {
 			}
 			continue
 		}
-		// Skip frontend rows + the "BACKEND" summary row — we want
-		// the per-server view ("L4OK", "L7OK", etc.).
 		svname := safeAt(fields, colIdx["svname"])
 		pxname := safeAt(fields, colIdx["pxname"])
-		if svname == "" || svname == "FRONTEND" || svname == "BACKEND" {
+
+		// Skip our internal stats listener and the BACKEND summary row.
+		if pxname == "internal_stats" || svname == "BACKEND" || svname == "" {
 			continue
 		}
-		// Skip our internal api_backend stats listener and frontends.
-		if pxname == "internal_stats" {
+
+		if svname == "FRONTEND" {
+			// Collect frontend (listener) counters.
+			frontends = append(frontends, frontendStat{
+				Name:     pxname,
+				Sessions: parseInt64(safeAt(fields, colIdx["scur"])),
+				MaxSess:  parseInt64(safeAt(fields, colIdx["smax"])),
+				BIn:      parseInt64(safeAt(fields, colIdx["bin"])),
+				BOut:     parseInt64(safeAt(fields, colIdx["bout"])),
+				ReqTot:   parseInt64(safeAt(fields, colIdx["req_tot"])),
+				ReqRate:  parseInt64(safeAt(fields, colIdx["req_rate"])),
+			})
 			continue
 		}
-		st := backendStat{
+
+		// Per-server backend row.
+		backends = append(backends, backendStat{
 			Backend:  pxname,
 			Server:   svname,
 			Status:   safeAt(fields, colIdx["status"]),
@@ -103,10 +129,9 @@ func (h *HAProxyStatsHandler) Stats(c *gin.Context) {
 			ReqRate:  parseInt64(safeAt(fields, colIdx["req_rate"])),
 			LastChg:  parseInt64(safeAt(fields, colIdx["lastchg"])),
 			Health:   safeAt(fields, colIdx["check_status"]),
-		}
-		out = append(out, st)
+		})
 	}
-	response.OK(c, gin.H{"backends": out})
+	response.OK(c, gin.H{"backends": backends, "frontends": frontends})
 }
 
 func safeAt(fields []string, i int) string {