feat(PROJ-28): SMTP-Out Relay — DB-Konfiguration + Admin-Tab

- smtpoutconfig.Store: AES-256-GCM verschlüsseltes Passwort in DB (id=1 Singleton)
- Mailer: Reload() für Runtime-Konfigurationswechsel (sync.RWMutex)
- API: GET/PUT/DELETE /api/admin/smtp-out + POST /api/admin/smtp-out/test
- Admin-Tab: Host, Port, User, Passwort, TLS-Switch, From, Test-Button, Status-Badge
- Startup: Lädt DB-Konfiguration und aktiviert Mailer ohne Restart

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

src/app/admin/page.tsx

@@ -78,6 +78,7 @@ import { ModulesTab } from "@/components/admin/ModulesTab";
 import { IMAPSettingsTab } from "@/components/admin/tabs/IMAPSettingsTab";
 import { RetentionTab } from "@/components/admin/tabs/RetentionTab";
 import { QuotaTab } from "@/components/admin/tabs/QuotaTab";
+import { SMTPOutTab } from "@/components/admin/tabs/SMTPOutTab";
 import { ResetPasswordDialog, DeleteUserDialog } from "@/components/admin/UserDialogs";
 
 const AUDIT_PAGE_SIZE = 25;
@@ -811,6 +812,7 @@ export default function AdminPage() {
             {isSuperAdmin && <TabsTrigger value="tenants" onClick={loadTenants}>Mandanten</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="retention">Retention</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="quotas">Quotas</TabsTrigger>}
+            {isSuperAdmin && <TabsTrigger value="smtp-out">SMTP-Out</TabsTrigger>}
             {isSuperAdmin && <TabsTrigger value="modules">Module</TabsTrigger>}
           </TabsList>
 
@@ -1100,6 +1102,11 @@ export default function AdminPage() {
             </TabsContent>
           )}
 
+          {isSuperAdmin && (
+            <TabsContent value="smtp-out">
+              <SMTPOutTab />
+            </TabsContent>
+          )}
           <TabsContent value="modules" className="mt-4">
             <ModulesTab />
           </TabsContent>