feat(PROJ-34): Retention-Tab + pro-Mandant Aufbewahrungsfristen

- tenantstore: retention_days Spalte, GetRetentionDays/SetRetentionDays
- storage.Save(): per-tenant retention überschreibt globale config
- API: GET /api/admin/retention, PUT /api/admin/tenant/{id}/retention
- Frontend: RetentionTab mit globaler Policy-Anzeige, Mandanten-Tabelle,
  Bearbeiten-Dialog und Purge-Button (superadmin only)

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

src/app/admin/page.tsx

@@ -76,6 +76,7 @@ import { LabelsTab } from "@/components/admin/tabs/LabelsTab";
 import { CertTab } from "@/components/admin/tabs/CertTab";
 import { ModulesTab } from "@/components/admin/ModulesTab";
 import { IMAPSettingsTab } from "@/components/admin/tabs/IMAPSettingsTab";
+import { RetentionTab } from "@/components/admin/tabs/RetentionTab";
 import { ResetPasswordDialog, DeleteUserDialog } from "@/components/admin/UserDialogs";
 
 const AUDIT_PAGE_SIZE = 25;
@@ -807,6 +808,7 @@ export default function AdminPage() {
             {isSuperAdmin && <TabsTrigger value="security">Security</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="cert" onClick={loadCert}>Zertifikat</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="tenants" onClick={loadTenants}>Mandanten</TabsTrigger>}
+            {isSuperAdmin && <TabsTrigger value="retention">Retention</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="modules">Module</TabsTrigger>}
           </TabsList>
 
@@ -1085,6 +1087,12 @@ export default function AdminPage() {
             </TabsContent>
           )}
 
+          {isSuperAdmin && (
+            <TabsContent value="retention">
+              <RetentionTab />
+            </TabsContent>
+          )}
+
           <TabsContent value="modules" className="mt-4">
             <ModulesTab />
           </TabsContent>

src/components/admin/tabs/RetentionTab.tsx

@@ -0,0 +1,279 @@
+"use client";
+
+import { useState, useEffect, useCallback } from "react";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Badge } from "@/components/ui/badge";
+import {
+  Table,
+  TableBody,
+  TableCell,
+  TableHead,
+  TableHeader,
+  TableRow,
+} from "@/components/ui/table";
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
+
+interface TenantRetention {
+  id: number;
+  name: string;
+  slug: string;
+  retention_days: number;
+}
+
+interface RetentionData {
+  global_retention_days: number;
+  tenants: TenantRetention[];
+}
+
+async function fetchRetention(): Promise<RetentionData> {
+  const res = await fetch("/api/admin/retention", { credentials: "include" });
+  if (!res.ok) throw new Error("Fehler beim Laden");
+  return res.json();
+}
+
+async function setTenantRetention(tenantID: number, days: number): Promise<void> {
+  const res = await fetch(`/api/admin/tenant/${tenantID}/retention`, {
+    method: "PUT",
+    credentials: "include",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ retention_days: days }),
+  });
+  if (!res.ok) {
+    const err = await res.json().catch(() => ({}));
+    throw new Error((err as { error?: string }).error ?? "Fehler beim Speichern");
+  }
+}
+
+async function triggerPurge(): Promise<number> {
+  const res = await fetch("/api/admin/purge", {
+    method: "POST",
+    credentials: "include",
+  });
+  if (!res.ok) throw new Error("Purge fehlgeschlagen");
+  const data = await res.json();
+  return data.deleted ?? 0;
+}
+
+function retentionLabel(days: number, globalDays: number): React.ReactNode {
+  if (days === 0) {
+    return globalDays > 0 ? (
+      <span className="text-muted-foreground text-sm">
+        Global ({globalDays} Tage)
+      </span>
+    ) : (
+      <Badge variant="secondary">Kein Lock</Badge>
+    );
+  }
+  return <Badge>{days} Tage</Badge>;
+}
+
+export function RetentionTab() {
+  const [data, setData] = useState<RetentionData | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState("");
+
+  // edit state
+  const [editTenant, setEditTenant] = useState<TenantRetention | null>(null);
+  const [editDays, setEditDays] = useState("");
+  const [saving, setSaving] = useState(false);
+
+  // purge state
+  const [purgeOpen, setPurgeOpen] = useState(false);
+  const [purging, setPurging] = useState(false);
+  const [purgeResult, setPurgeResult] = useState<number | null>(null);
+
+  const load = useCallback(() => {
+    setLoading(true);
+    fetchRetention()
+      .then(setData)
+      .catch(() => setError("Retention-Daten konnten nicht geladen werden"))
+      .finally(() => setLoading(false));
+  }, []);
+
+  useEffect(() => { load(); }, [load]);
+
+  const handleEditOpen = (t: TenantRetention) => {
+    setEditTenant(t);
+    setEditDays(t.retention_days > 0 ? String(t.retention_days) : "");
+    setSaving(false);
+  };
+
+  const handleEditSave = async () => {
+    if (!editTenant) return;
+    const days = editDays.trim() === "" ? 0 : parseInt(editDays, 10);
+    if (isNaN(days) || days < 0) return;
+    setSaving(true);
+    try {
+      await setTenantRetention(editTenant.id, days);
+      setEditTenant(null);
+      load();
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Fehler");
+    } finally {
+      setSaving(false);
+    }
+  };
+
+  const handlePurge = async () => {
+    setPurging(true);
+    setPurgeResult(null);
+    try {
+      const deleted = await triggerPurge();
+      setPurgeResult(deleted);
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Purge fehlgeschlagen");
+      setPurgeOpen(false);
+    } finally {
+      setPurging(false);
+    }
+  };
+
+  const globalDays = data?.global_retention_days ?? 0;
+
+  return (
+    <div className="mt-4 space-y-4">
+      {/* Global Policy */}
+      <Card>
+        <CardHeader>
+          <CardTitle>Globale Retention-Policy</CardTitle>
+        </CardHeader>
+        <CardContent className="space-y-3">
+          <div className="flex items-center gap-3">
+            <span className="text-sm font-medium">Globale Aufbewahrungsfrist:</span>
+            {globalDays > 0 ? (
+              <Badge>{globalDays} Tage ({Math.round(globalDays / 365)} Jahre)</Badge>
+            ) : (
+              <Badge variant="secondary">Kein globaler Lock (config.yml)</Badge>
+            )}
+          </div>
+          <p className="text-sm text-muted-foreground">
+            Die globale Frist wird in <code className="text-xs bg-muted px-1 rounded">config.yml → storage.retention_days</code> konfiguriert.
+            Mandanten-spezifische Einstellungen überschreiben diese, wenn gesetzt.
+          </p>
+          <Button
+            variant="destructive"
+            size="sm"
+            onClick={() => { setPurgeOpen(true); setPurgeResult(null); }}
+          >
+            Abgelaufene Mails jetzt löschen (Purge)
+          </Button>
+          {error && <p className="text-sm text-destructive">{error}</p>}
+        </CardContent>
+      </Card>
+
+      {/* Per-tenant table */}
+      <Card>
+        <CardHeader>
+          <CardTitle>Retention pro Mandant</CardTitle>
+        </CardHeader>
+        <CardContent>
+          {loading ? (
+            <p className="text-sm text-muted-foreground">Lädt...</p>
+          ) : (
+            <Table>
+              <TableHeader>
+                <TableRow>
+                  <TableHead>Mandant</TableHead>
+                  <TableHead>Aufbewahrungsfrist</TableHead>
+                  <TableHead className="w-24"></TableHead>
+                </TableRow>
+              </TableHeader>
+              <TableBody>
+                {(data?.tenants ?? []).map((t) => (
+                  <TableRow key={t.id}>
+                    <TableCell className="font-medium">{t.name}</TableCell>
+                    <TableCell>{retentionLabel(t.retention_days, globalDays)}</TableCell>
+                    <TableCell>
+                      <Button size="sm" variant="outline" onClick={() => handleEditOpen(t)}>
+                        Bearbeiten
+                      </Button>
+                    </TableCell>
+                  </TableRow>
+                ))}
+              </TableBody>
+            </Table>
+          )}
+        </CardContent>
+      </Card>
+
+      {/* Edit Dialog */}
+      <Dialog open={!!editTenant} onOpenChange={(o) => { if (!o) setEditTenant(null); }}>
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>Retention für &quot;{editTenant?.name}&quot;</DialogTitle>
+            <DialogDescription>
+              Aufbewahrungsfrist in Tagen. <strong>0</strong> = globale Einstellung verwenden.
+              GoBD: mind. 10 Jahre = 3650 Tage.
+            </DialogDescription>
+          </DialogHeader>
+          <div className="space-y-2 py-2">
+            <label className="text-sm font-medium">Aufbewahrung (Tage)</label>
+            <Input
+              type="number"
+              min={0}
+              placeholder="0 = globale Einstellung"
+              value={editDays}
+              onChange={(e) => setEditDays(e.target.value)}
+            />
+            {editDays && parseInt(editDays) > 0 && (
+              <p className="text-xs text-muted-foreground">
+                ≈ {(parseInt(editDays) / 365).toFixed(1)} Jahre
+              </p>
+            )}
+          </div>
+          <DialogFooter>
+            <Button variant="outline" onClick={() => setEditTenant(null)}>
+              Abbrechen
+            </Button>
+            <Button disabled={saving} onClick={handleEditSave}>
+              {saving ? "Speichern..." : "Speichern"}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+
+      {/* Purge Dialog */}
+      <Dialog open={purgeOpen} onOpenChange={setPurgeOpen}>
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>Abgelaufene Mails löschen</DialogTitle>
+            <DialogDescription>
+              Alle Mails, deren Aufbewahrungsfrist abgelaufen ist, werden unwiderruflich gelöscht.
+              Mails innerhalb der Frist bleiben erhalten.
+            </DialogDescription>
+          </DialogHeader>
+          {purgeResult !== null ? (
+            <p className="text-sm font-medium py-2">
+              {purgeResult === 0
+                ? "Keine abgelaufenen Mails gefunden."
+                : `${purgeResult} Mail(s) erfolgreich gelöscht.`}
+            </p>
+          ) : (
+            <p className="text-sm text-muted-foreground py-2">
+              Dieser Vorgang kann nicht rückgängig gemacht werden.
+            </p>
+          )}
+          <DialogFooter>
+            <Button variant="outline" onClick={() => setPurgeOpen(false)}>
+              {purgeResult !== null ? "Schließen" : "Abbrechen"}
+            </Button>
+            {purgeResult === null && (
+              <Button variant="destructive" disabled={purging} onClick={handlePurge}>
+                {purging ? "Lösche..." : "Jetzt löschen"}
+              </Button>
+            )}
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+    </div>
+  );
+}