fix(07): UAT fixes — SMTP test email, DKV routing, Exchange domain field

- SMTP: add test-to field, send real email via sendMail() instead of verify()
- SMTP: fix no_auth warning shown as error for open-relay servers
- DKV: register dkv-fleet in MODULE_REGISTRY (fixes "Modul nicht gefunden")
- DKV: add dynamic [category]/[moduleSlug]/settings + vehicles sub-routes
- DKV: settings/vehicles links use useParams for consistent URLs
- DKV: add gear icon settings link to module main page
- DKV: rename module to "DKV-Rechnung" in seed + translations
- DKV: add optional domain field for Exchange (WebCredentials 3rd arg)
- DKV: hide IMAP-only fields (Port/Verschlüsselung/Ordner) when Exchange selected
- DKV: hide Exchange-only field (Domain) when IMAP selected
- Prisma: add domain column to DkvModuleConfig

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

apps/web/src/app/(portal)/modules/dkv-fleet/page.tsx

@@ -2,6 +2,8 @@
 
 import { useCallback, useState } from 'react';
 import { useTranslations } from 'next-intl';
+import { useParams } from 'next/navigation';
+import Link from 'next/link';
 import { checkNow, type DkvHistoryEntry } from '@/lib/dkv-api';
 import { InvoiceHistoryTable } from './components/InvoiceHistoryTable';
 import { ExportFileList } from './components/ExportFileList';
@@ -33,6 +35,10 @@ function SpinnerIcon() {
  */
 export default function DkvFleetPage() {
   const t = useTranslations('dkvFleet');
+  const params = useParams<{ category?: string; moduleSlug?: string }>();
+  const basePath = params.category && params.moduleSlug
+    ? `/modules/${params.category}/${params.moduleSlug}`
+    : '/modules/dkv-fleet';
 
   const [isChecking, setIsChecking] = useState(false);
   const [pollError, setPollError] = useState<string | null>(null);
@@ -83,6 +89,18 @@ export default function DkvFleetPage() {
           </p>
         </div>
 
+        {/* Einstellungen-Link */}
+        <Link
+          href={`${basePath}/settings`}
+          className="rounded border border-border px-3 py-2 text-sm text-muted-foreground transition-colors hover:bg-muted hover:text-foreground"
+          title={t('settingsTitle')}
+        >
+          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" aria-hidden="true">
+            <circle cx="12" cy="12" r="3" />
+            <path d="M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 0 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 0 1-2.83-2.83l.06-.06A1.65 1.65 0 0 0 4.68 15a1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 0 1 2.83-2.83l.06.06A1.65 1.65 0 0 0 9 4.68a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 0 1 2.83 2.83l-.06.06A1.65 1.65 0 0 0 19.4 9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z" />
+          </svg>
+        </Link>
+
         {/* "Jetzt prüfen" button per 07-UI-SPEC button states */}
         <button
           type="button"