feat(PROJ-39): eDiscovery Export + Feature-Specs PROJ-40–43

- Neuer POST /api/export/ediscovery Handler (internal/api/ediscovery.go)
- Route in server.go registriert
- Feature-Specs PROJ-39 bis PROJ-43 angelegt
- INDEX.md aktualisiert

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

internal/api/server.go

@@ -235,6 +235,7 @@ func (s *Server) routes() {
 	// Export routes
 	s.mux.HandleFunc("GET /api/export/pdf/{id}", s.auth(s.requireMailAccess(s.handleExportPDF)))
 	s.mux.HandleFunc("POST /api/export/zip", s.auth(s.requireMailAccess(s.handleExportZIP)))
+	s.mux.HandleFunc("POST /api/export/ediscovery", s.auth(s.handleExportEDiscovery))
 
 	// Upload routes (admin only)
 	s.mux.HandleFunc("POST /api/admin/upload", s.authAdmin(s.handleUpload))