fix(PROJ-30): ListFolders — c.Client statt c uebergeben (imap.Conn vs *imapclient.Client)

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

internal/api/import_handlers.go

@@ -159,7 +159,7 @@ func (s *Server) handleTestImap(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	folders, err := imapstore.ListFolders(c)
+	folders, err := imapstore.ListFolders(c.Client)
 	if err != nil {
 		writeJSON(w, http.StatusOK, map[string]interface{}{
 			"ok":    false,