Server actions crash when current workflow has no fileName (unsaved/new tab)

[Titas-Ghosh]

If server actions are triggered from a new/unsaved workflow tab, the app can crash because action methods assume fileName always exists and call fileName.split('.')

This happens in build, debug, run, clear, stop, and destroy paths in 6-server.js

When no GraphML file is loaded for the current workflow, server actions should fail gracefully with a clear message (for example: “Open a GraphML file before using server actions.”), without throwing runtime errors.

i think this is a substantial user facing stability issue cause a normal UI action can crash the flow on fresh tabs and creates confusion around server side features.