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>

internal/api/server.go

@@ -13,6 +13,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -45,6 +46,7 @@ type Server struct {
 	imapStore     *imapstore.Store
 	imapImporter  *imapstore.Importer
 	imapScheduler *imapstore.Scheduler
+	uploadJobs    sync.Map // jobID → *UploadJob
 }
 
 // SetSMTPDaemon wires the SMTP daemon into the API server after construction.
@@ -108,6 +110,10 @@ func (s *Server) routes() {
 	s.mux.HandleFunc("GET /api/export/pdf/{id}", s.authMiddleware(s.requireMailAccess(s.handleExportPDF)))
 	s.mux.HandleFunc("POST /api/export/zip", s.authMiddleware(s.requireMailAccess(s.handleExportZIP)))
 
+	// Upload routes (admin only)
+	s.mux.HandleFunc("POST /api/admin/upload", s.authMiddleware(s.requireRole(userstore.RoleAdmin, s.handleUpload)))
+	s.mux.HandleFunc("GET /api/admin/upload/{jobID}/progress", s.authMiddleware(s.requireRole(userstore.RoleAdmin, s.handleUploadProgress)))
+
 	// IMAP routes (accessible to all authenticated users)
 	s.mux.HandleFunc("GET /api/imap", s.authMiddleware(s.handleListImap))
 	s.mux.HandleFunc("POST /api/imap", s.authMiddleware(s.handleCreateImap))