[Notebook Migration] Upload notebooks under a per-workflow filename

[zyratlo]

Feature Summary

The frontend uploads every workflow's notebook to a fixed path, work/notebook.ipynb. This is safe across users under the per-user-pod model, but not across one user's workflows: they all land on the same file, so switching workflows overwrites it. Two tabs open on different workflows collide on the same file while each keeps its own cell-to-operator highlight mapping.

Use a per-workflow filename so each workflow's notebook is distinct.

A related cleanup: the comment on the fixed filename in sendNotebookToJupyter still references the backend's process-global jupyterIframeURL, which was removed in #7602. It should be corrected as part of this change.

Proposed Solution or Design

Thread a per-workflow notebook name through both the upload and the iframe fetch, keyed by the workflow id (for example notebook_<wid>.ipynb, which already passes the backend's filename validation):

• NotebookMigrationService.sendNotebookToJupyter takes an explicit notebook name instead of hardcoding notebook.ipynb.
• NotebookMigrationService.getJupyterIframeURL passes the same name as the notebookName query parameter that the backend now accepts (added in feat(notebook-migration-service): compute jupyter iframe url per request #7602).
• JupyterPanelService owns the name derivation from the current workflow id and passes it on both the upload and the iframe fetch, so the two always agree.
• Update the consumer specs to cover the per-workflow name on both paths.

The backend already supports this: #7602 made get-jupyter-iframe-url accept an optional notebookName, and set-notebook accepts any valid .ipynb name. No backend change is required.

Affected Area

Workflow UI

[zyratlo]

/parent-issue #4301