feat: double-click a sidebar row to rename it in place

Notebooks, section groups and sections rename in their rows, as the Finder
renames a file. A notebook takes the name as OK in Notebook Properties gives
it: its folder is renamed where it can be, else its display name. The double
click's first click no longer leaves a notebook or group folded.

Assisted-by: claude-opus-5.5
0f9f47a89fclover caruso committed on 10/3/2026, 2:05:30 PMparent5e10e17
3 files changedLine totals unavailable