docs: vollständige README, PROJ-2 Web-Upload, PROJ-19 Mailpiler-Migration

README.md:
- Vollständige Dokumentation aller implementierten Funktionen
- Konfigurationsreferenz, Installation, Systemd, REST-API-Übersicht
- In-Progress-Features klar gekennzeichnet

PROJ-2 (EML/MBOX Web-Upload):
- POST /api/admin/upload – Multipart-Upload mit Hintergrund-Job
- GET /api/admin/upload/{jobID}/progress – Polling
- Admin-Tab "Import" mit Drag-and-Drop, Fortschrittsbalken, Abschlussbericht

PROJ-19 (Mailpiler Migration):
- archivmail import-piler mit Methoden: pilerexport | direct | auto
- Direct: AES-256-CBC + zlib mit defensiven Fallbacks
- pilerexport: Wrapper um mailpilers Export-Tool

Status-Updates: PROJ-3, PROJ-4, PROJ-6, PROJ-7, PROJ-10, PROJ-11 → Deployed

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

src/lib/api.ts

@@ -453,3 +453,34 @@ export async function exportMailsZIP(ids: string[], attachments: boolean): Promi
   if (!res.ok) throw new Error("ZIP export failed");
   return { blob: await res.blob() };
 }
+
+// ── Upload ────────────────────────────────────────────────────────────────
+
+export interface UploadJob {
+  id: string;
+  status: "running" | "done" | "error";
+  total: number;
+  imported: number;
+  skipped: number;
+  errors: number;
+  error_msg?: string;
+}
+
+export async function uploadMailFiles(files: File[]): Promise<{ job_id: string }> {
+  const form = new FormData();
+  for (const f of files) form.append("files", f);
+  const res = await fetch(`${API_BASE}/api/admin/upload`, {
+    method: "POST",
+    credentials: "include",
+    body: form,
+  });
+  if (!res.ok) {
+    const body = await res.text();
+    throw new Error(body || `Upload failed: ${res.status}`);
+  }
+  return res.json();
+}
+
+export async function getUploadProgress(jobID: string): Promise<UploadJob> {
+  return request<UploadJob>(`/api/admin/upload/${jobID}/progress`);
+}