feat(PROJ-18): E-Mail Integritätsprüfung (SHA-256 Verifikation)

- Storage: VerifyIntegrity, GetAllIDs, GetVerifyStatus + DB-Spalten
- main: Hintergrund-Worker alle 5 Minuten (beim Start sofort: 40/40 OK)
- API: verify_ok + verified_at in GET /api/mails/{id} Antwort
- Frontend: Grüner Haken / graues X / rotes X in Mail-Ansicht

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

src/app/mail/[id]/page.tsx

@@ -83,6 +83,32 @@ function MailHeaderGrid({ mail }: { mail: MailDetail }) {
         <span className="font-semibold">{mail.subject || "(kein Betreff)"}</span>
         <span className="font-medium text-muted-foreground">Größe:</span>
         <span>{formatBytes(mail.size)}</span>
+        {/* Verification status */}
+        <span className="font-medium text-muted-foreground">Integrität:</span>
+        <span>
+          {mail.verify_ok === true ? (
+            <span className="inline-flex items-center gap-1 text-green-600 text-sm font-medium">
+              <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M5 13l4 4L19 7" />
+              </svg>
+              Verifiziert
+            </span>
+          ) : mail.verify_ok === false ? (
+            <span className="inline-flex items-center gap-1 text-red-600 text-sm font-medium">
+              <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 18L18 6M6 6l12 12" />
+              </svg>
+              Manipuliert!
+            </span>
+          ) : (
+            <span className="inline-flex items-center gap-1 text-muted-foreground text-sm">
+              <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 18L18 6M6 6l12 12" />
+              </svg>
+              Noch nicht geprüft
+            </span>
+          )}
+        </span>
       </div>
 
       <button

src/lib/api.ts

@@ -112,6 +112,8 @@ export interface MailDetail {
   body_plain?: string;
   raw_headers: string;
   attachments: MailAttachment[];
+  verify_ok: boolean | null;
+  verified_at: string | null;
 }
 
 export interface AuditEntry {