[Notebook Migration] Make Jupyter microservice read-only and clean up UI

[zyratlo]

Task Summary

The notebook migration service generates a Jupyter notebook and embeds it in the Texera app as a reference view of the migrated workflow. It is meant for reading, not editing. The embedded container currently ships the classic Jupyter Notebook UI as is, which exposes editing and execution controls that do not belong in a reference view.

Problems

• The classic Notebook chrome (header with logo and logout, kernel and trust indicators, the File/Edit/View menu, and the toolbar) is visible inside the embed, even though none of it is relevant to viewing a generated notebook.
• Cells can be edited and executed. A user can click into a code cell and type, run cells, or double-click a markdown cell to drop it into its editable source view. None of that should be possible in a reference view.
• A second, non-functional scrollbar appears because both the document and the inner #site container scroll.

Proposed change

Configure the embedded Jupyter container so the notebook renders as a clean, read-only view:

• Hide the classic Notebook chrome so only the notebook cells remain.
• Lock the notebook: make code cell editors read-only, disable keyboard shortcuts so cells cannot be edited or executed, and keep markdown cells rendered.
• Fix the layout so there is a single working scrollbar.

This is scoped to the notebook migration service container assets only. It does not change the Texera frontend or backend.

Task Type

• Refactor / Cleanup
• DevOps / Deployment / CI
• Testing / QA
• Documentation
• Performance
• Other

[zyratlo]

/parent-issue #4301