feat(backup): download the full backup as ZIP

GET /export?format=zip streams the JSON backup compressed (plain JSON stays
the API default). The MindSift import recognises the backup ZIP next to the
plain JSON and the Markdown archive.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/server.go

@@ -2159,12 +2159,7 @@ func (s *Server) handleImportMindSift(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
-	if strings.HasSuffix(strings.ToLower(name), ".json") || (len(data) > 0 && data[0] == '{') {
-		plan, err := storage.PlanMindSiftJSONImport(data)
-		s.runImport(w, r, plan, err)
-		return
-	}
-	plan, err := storage.PlanMindSiftArchiveImport(bytes.NewReader(data), int64(len(data)))
+	plan, err := storage.PlanMindSiftImport(data, name)
 	s.runImport(w, r, plan, err)
 }
 
@@ -2197,6 +2192,15 @@ func (s *Server) handleExport(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
 	}
+	// ?format=zip: the same JSON compressed (backups grow quickly with notes); plain JSON stays the API default
+	if r.URL.Query().Get("format") == "zip" {
+		w.Header().Set("Content-Type", "application/zip")
+		w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="mindsift-backup-%s.zip"`, time.Now().Format("2006-01-02")))
+		if err := storage.WriteBackupZip(exportData, w); err != nil {
+			slog.Error("Backup-Export fehlgeschlagen", "user_id", userID, "error", err)
+		}
+		return
+	}
 	w.Header().Set("Content-Disposition", "attachment; filename=mindsift-export.json")
 	writeJSON(w, http.StatusOK, exportData)
 }