NotebookEdit tool behavior

NotebookEdit modifies a Jupyter notebook one cell at a time, targeting cells by their cell_id. It doesn't perform string replacement across the notebook the way Edit does on plain files.

Three edit modes control what happens to the target cell:

• replace: overwrite the cell's source. This is the default.
• insert: add a new cell after the target. With no cell_id, the new cell goes at the start of the notebook. Requires cell_type set to code or markdown.
• delete: remove the target cell.

Permission rules use the Edit(...) path format. A rule like Edit(notebooks/**) covers NotebookEdit calls on files in that directory.