CSV Export/Import: Time settings are unclear and inconsistent when importing nodes

### What is the input mode? Mouse ### What type of issue is it? Functionality ### What happened? When nodes are imported via CSV, it is not clear which time values are actually imported from the CSV file and which ones are automatically added by the system. In particular, when a node is exported with the setting “no stop”, the re-import does not behave transparently: - Instead of keeping the exported values, - the system appears to add generic or default time values, similar to what happens when a node is newly created via the UI. As a result, imported node time settings do not reliably reflect the original CSV data. <img width="1524" height="766" alt="Image" src="https://github.com/user-attachments/assets/d8211446-85e9-44ff-a299-7e28fef90946" /> ### What did you expect to happen? It should be clearly defined and reproducible which time values are taken from the CSV and which are computed or added by the system When exporting nodes with “no stop”, no random or generic default times should be added on import In this case, the system should store zero values internally for the relevant times CSV import/export should be lossless and predictable ### How can we reproduce it (as minimally and precisely as possible)? 1. Open a project with existing nodes 2. Configure a node with “no stop” 3. Go to Base data → Export base data 4. Export the nodes as a CSV file 5. Go to Base data → Import base data 6. Import the previously exported CSV 7 .Inspect the imported node’s time settings ### On which environments the bug occurs? Local ### On which browser the bug occurs? Firefox, Opera, Safari, Microsoft Edge, Google Chrome ### Netzgrafik-Editor version (top left corner `Version x.yy.zz`) 2.10.8