fix(dkv): fix inbox processing pipeline — orphan tenant, MIME detection, UNSEEN filter

- Fix orphaned DkvModuleConfig: tenantId pointed to deleted tenant, updated to Default tenant
- DKV controller: return 404 instead of HTTP 200 null when no config exists
- IMAP provider: also detect PDFs sent as application/octet-stream (check filename extension)
- IMAP provider: add seen:false filter so already-processed emails are skipped on re-poll
- IMAP provider: mark email as \Seen after successful PDF download to prevent reprocessing
- Frontend dkv-api: handle 404 from fetchConfig as "not yet configured" (returns null)
- InboxConfigForm: show warning banner when config not yet saved in DB
- InboxConfigForm: add "Jetzt prüfen" button to manually trigger POST /dkv/check-now

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

apps/web/src/app/(portal)/modules/dkv-fleet/settings/components/InboxConfigForm.tsx

@@ -4,6 +4,7 @@ import { useCallback, useEffect, useState } from 'react';
 import { useTranslations } from 'next-intl';
 import {
   type DkvConfig,
+  checkNow,
   fetchConfig,
   saveConfig,
   testConnection,
@@ -154,14 +155,24 @@ export function InboxConfigForm() {
   const [saveError, setSaveError] = useState<string | null>(null);
   const [saveSuccess, setSaveSuccess] = useState(false);
 
+  // Check-now state
+  const [isChecking, setIsChecking] = useState(false);
+  const [checkResult, setCheckResult] = useState<{ status: string; message: string } | null>(null);
+
+  // Whether config exists in DB (null = not yet saved)
+  const [configExists, setConfigExists] = useState(false);
+
   // Load config on mount
   useEffect(() => {
     fetchConfig()
       .then((config) => {
-        setForm(configToForm(config));
+        if (config) {
+          setForm(configToForm(config));
+          setConfigExists(true);
+        }
       })
       .catch(() => {
-        // Keep defaults if config not yet created
+        // Keep defaults if fetch failed
       })
       .finally(() => {
         setIsLoading(false);
@@ -201,6 +212,7 @@ export function InboxConfigForm() {
     try {
       await saveConfig(formToPayload(form));
       setSaveSuccess(true);
+      setConfigExists(true);
       // Clear password field after save (T-07-12)
       setForm((f) => ({ ...f, password: '' }));
     } catch (err) {
@@ -212,6 +224,22 @@ export function InboxConfigForm() {
     }
   };
 
+  const handleCheckNow = async () => {
+    setIsChecking(true);
+    setCheckResult(null);
+    try {
+      const result = await checkNow();
+      setCheckResult(result);
+    } catch (err) {
+      setCheckResult({
+        status: 'error',
+        message: err instanceof Error ? err.message : 'Fehler beim Abrufen',
+      });
+    } finally {
+      setIsChecking(false);
+    }
+  };
+
   const inputCls =
     'h-9 w-full max-w-md rounded border border-border bg-background px-3 text-sm text-foreground';
   const labelCls = 'mb-1 block text-sm text-foreground';
@@ -231,6 +259,12 @@ export function InboxConfigForm() {
 
   return (
     <div className="space-y-4">
+      {/* Banner: config not yet saved */}
+      {!configExists && (
+        <div className="rounded-md border border-amber-300 bg-amber-50 px-4 py-3 text-sm text-amber-800 dark:border-amber-700 dark:bg-amber-900/20 dark:text-amber-300">
+          Noch nicht gespeichert — Konfiguration ausfüllen und speichern.
+        </div>
+      )}
       {/* Protokoll */}
       <div>
         <label htmlFor="dkv-protocol" className={labelCls}>
@@ -503,8 +537,28 @@ export function InboxConfigForm() {
         >
           {t('form.save')}
         </button>
+        {configExists && (
+          <button
+            type="button"
+            onClick={handleCheckNow}
+            disabled={isChecking || isSaving || isTesting}
+            className="rounded border border-border px-4 py-2 text-sm text-foreground transition-colors hover:bg-muted disabled:opacity-50 disabled:cursor-not-allowed"
+          >
+            {isChecking ? 'Prüfe...' : 'Jetzt prüfen'}
+          </button>
+        )}
       </div>
 
+      {/* Check-now result */}
+      {checkResult && (
+        <p
+          className="text-sm"
+          style={{ color: checkResult.status === 'ok' ? 'oklch(0.40 0.15 148)' : 'var(--destructive)' }}
+        >
+          {checkResult.status === 'ok' ? `✓ ${checkResult.message}` : `✗ ${checkResult.message}`}
+        </p>
+      )}
+
       {/* Inline test feedback */}
       {testResult !== null && (
         <div className="space-y-1">

apps/web/src/lib/dkv-api.ts

@@ -95,10 +95,11 @@ export interface DkvHistoryPage {
  * Fetch the current DKV module inbox configuration.
  * GET /dkv/config
  */
-export async function fetchConfig(): Promise<DkvConfig> {
+export async function fetchConfig(): Promise<DkvConfig | null> {
   const res = await fetch(`${API_URL}/dkv/config`, {
     credentials: 'include',
   });
+  if (res.status === 404) return null;
   if (!res.ok) throw new Error('Failed to fetch DKV config');
   return res.json();
 }
@@ -143,12 +144,13 @@ export async function testConnection(
  * Trigger an immediate inbox check (manual poll).
  * POST /dkv/check-now
  */
-export async function checkNow(): Promise<void> {
+export async function checkNow(): Promise<{ status: string; message: string; checkedAt: string }> {
   const res = await fetch(`${API_URL}/dkv/check-now`, {
     method: 'POST',
     credentials: 'include',
   });
   if (!res.ok) throw new Error('Failed to trigger DKV inbox check');
+  return res.json();
 }
 
 /**