feat: Dashboard-Metriken nach Mailpiler-Vorbild (Uptime, Aktivität, Prognose)

- storage_stats.go (neu): MailActivityStats (60min/24h/7d/30d), StorageEstimateStats
- dashboard_handlers.go: Uptime (/proc/uptime), activity + estimate in System-Stats-Response
- DashboardTab: Uptime in API-Kachel, neue Kacheln "Mail-Eingang" + "Speicherprognose"
- Warnung (Badge "Knapp!") wenn Partition in <90 Tagen voll

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

src/components/admin/tabs/DashboardTab.tsx

@@ -4,6 +4,8 @@ import {
   type SMTPStatus,
   type StorageStats,
   type SystemStats,
+  type SystemStatsActivity,
+  type SystemStatsEstimate,
 } from "@/lib/api";
 import { type User } from "@/lib/api";
 import { Button } from "@/components/ui/button";
@@ -20,6 +22,73 @@ function formatBytes(bytes: number): string {
   return `${(bytes / (1024 * 1024 * 1024)).toFixed(2)} GB`;
 }
 
+function formatUptime(seconds: number): string {
+  const d = Math.floor(seconds / 86400);
+  const h = Math.floor((seconds % 86400) / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  if (d > 0) return `${d}d ${h}h ${m}m`;
+  if (h > 0) return `${h}h ${m}m`;
+  return `${m}m`;
+}
+
+function formatDaysUntilFull(days: number): string {
+  if (days < 0) return "∞";
+  if (days < 30) return `${days} Tage`;
+  if (days < 365) return `${Math.round(days / 30)} Monate`;
+  return `${(days / 365).toFixed(1)} Jahre`;
+}
+
+function ActivityCard({ activity }: { activity: SystemStatsActivity }) {
+  return (
+    <Card>
+      <CardContent className="pt-6 space-y-3">
+        <div className="flex items-center justify-between">
+          <span className="text-sm font-medium text-muted-foreground">Mail-Eingang</span>
+        </div>
+        <Separator />
+        <div className="grid grid-cols-2 gap-1 text-sm">
+          <span className="text-muted-foreground">Letzte 60 min</span>
+          <span className="font-semibold">{activity.last_60_min.toLocaleString("de-DE")}</span>
+          <span className="text-muted-foreground">Letzte 24 h</span>
+          <span className="font-semibold">{activity.last_24h.toLocaleString("de-DE")}</span>
+          <span className="text-muted-foreground">Letzte 7 Tage</span>
+          <span className="font-semibold">{activity.last_7d.toLocaleString("de-DE")}</span>
+          <span className="text-muted-foreground">Letzte 30 Tage</span>
+          <span className="font-semibold">{activity.last_30d.toLocaleString("de-DE")}</span>
+        </div>
+      </CardContent>
+    </Card>
+  );
+}
+
+function EstimateCard({ estimate }: { estimate: SystemStatsEstimate }) {
+  return (
+    <Card>
+      <CardContent className="pt-6 space-y-3">
+        <div className="flex items-center justify-between">
+          <span className="text-sm font-medium text-muted-foreground">Speicherprognose</span>
+          {estimate.days_until_full >= 0 && estimate.days_until_full < 90 && (
+            <Badge variant="destructive">Knapp!</Badge>
+          )}
+        </div>
+        <Separator />
+        <div className="grid grid-cols-2 gap-1 text-sm">
+          <span className="text-muted-foreground">Ø Mails/Tag</span>
+          <span className="font-semibold">{estimate.avg_mails_per_day.toFixed(1)}</span>
+          <span className="text-muted-foreground">Ø Mail-Größe</span>
+          <span>{formatBytes(estimate.avg_mail_bytes)}</span>
+          <span className="text-muted-foreground">Archiv-Alter</span>
+          <span>{estimate.archive_age_days} Tage</span>
+          <span className="text-muted-foreground">Partition voll in</span>
+          <span className={estimate.days_until_full >= 0 && estimate.days_until_full < 90 ? "font-semibold text-destructive" : "font-semibold"}>
+            {formatDaysUntilFull(estimate.days_until_full)}
+          </span>
+        </div>
+      </CardContent>
+    </Card>
+  );
+}
+
 interface DashboardTabProps {
   isSuperAdmin: boolean;
   smtpStatus: SMTPStatus | null;
@@ -74,7 +143,7 @@ export function DashboardTab({
           {/* Status-Kacheln */}
           <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-3">
 
-            {/* API */}
+            {/* API + Uptime */}
             <Card>
               <CardContent className="pt-6 space-y-3">
                 <div className="flex items-center justify-between">
@@ -89,6 +158,12 @@ export function DashboardTab({
                   <span className="font-mono">:8080</span>
                   <span className="text-muted-foreground">Protokoll</span>
                   <span>HTTP</span>
+                  {systemStats?.uptime && (
+                    <>
+                      <span className="text-muted-foreground">System-Uptime</span>
+                      <span>{formatUptime(systemStats.uptime.seconds)}</span>
+                    </>
+                  )}
                 </div>
               </CardContent>
             </Card>
@@ -293,6 +368,17 @@ export function DashboardTab({
                   </Card>
                 </div>
 
+                {/* Mail-Aktivität + Speicherprognose */}
+                {(systemStats.activity || systemStats.estimate) && (
+                  <div className="space-y-2">
+                    <h3 className="text-sm font-semibold text-muted-foreground uppercase tracking-wide">Archiv-Statistik</h3>
+                    <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-3">
+                      {systemStats.activity && <ActivityCard activity={systemStats.activity} />}
+                      {systemStats.estimate && <EstimateCard estimate={systemStats.estimate} />}
+                    </div>
+                  </div>
+                )}
+
                 {/* Festplatten */}
                 {systemStats.disks.length > 0 && (
                   <div className="space-y-2">

src/lib/api/index.ts

@@ -123,6 +123,8 @@ export type {
   SystemStatsRAM,
   SystemStatsDisk,
   SystemStatsMailInfo,
+  SystemStatsActivity,
+  SystemStatsEstimate,
   SystemStats,
   SecurityCheck,
   SecurityAuditResult,

src/lib/api/system.ts

@@ -83,14 +83,31 @@ export interface SystemStatsMailInfo {
   subject: string;
 }
 
+export interface SystemStatsActivity {
+  last_60_min: number;
+  last_24h: number;
+  last_7d: number;
+  last_30d: number;
+}
+
+export interface SystemStatsEstimate {
+  avg_mails_per_day: number;
+  avg_mail_bytes: number;
+  days_until_full: number; // -1 = unknown
+  archive_age_days: number;
+}
+
 export interface SystemStats {
   cpu: SystemStatsCPU;
   ram: SystemStatsRAM;
   disks: SystemStatsDisk[];
+  uptime: { seconds: number };
   archive: {
     first_mail: SystemStatsMailInfo | null;
     last_mail: SystemStatsMailInfo | null;
   };
+  activity: SystemStatsActivity;
+  estimate: SystemStatsEstimate;
 }
 
 export interface SecurityCheck {