feat(PROJ-12): E-Mail Export EML/PDF/ZIP

- GET /api/export/pdf/{id}: PDF-Generierung (stdlib, kein ext. Paket)
- POST /api/export/zip: Streaming-ZIP mit manifest.csv, Anhänge optional
- Max. 500 Mails pro Export, Zugriffscheck per Rolle
- Audit-Log für jeden Export
- Frontend: PDF-Button in Mail-Ansicht
- Frontend: Checkboxen + ZIP-Export-Dialog in Suchergebnissen

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

src/lib/api.ts

@@ -391,3 +391,32 @@ export interface SystemStats {
 export async function getSystemStats(): Promise<SystemStats> {
   return request<SystemStats>("/api/admin/system/stats");
 }
+
+// ── Export ────────────────────────────────────────────────────────────────
+
+export async function exportMailPDF(id: string): Promise<{ blob: Blob; filename: string }> {
+  const token = getToken();
+  const res = await fetch(`${API_BASE}/api/export/pdf/${id}`, {
+    headers: token ? { Authorization: `Bearer ${token}` } : {},
+  });
+  if (!res.ok) throw new Error("PDF export failed");
+  const blob = await res.blob();
+  const cd = res.headers.get("Content-Disposition") || "";
+  const filename = cd.match(/filename="([^"]+)"/)?.[1] || `${id.slice(0, 16)}.pdf`;
+  return { blob, filename };
+}
+
+export async function exportMailsZIP(ids: string[], attachments: boolean): Promise<{ blob: Blob }> {
+  const token = getToken();
+  const res = await fetch(`${API_BASE}/api/export/zip`, {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/json",
+      ...(token ? { Authorization: `Bearer ${token}` } : {}),
+    },
+    body: JSON.stringify({ ids, attachments }),
+  });
+  if (!res.ok) throw new Error("ZIP export failed");
+  const blob = await res.blob();
+  return { blob };
+}