[datlechin]

Why

• A grid column could be resized only by dragging its header's edge, so a keyboard-only user could not widen a column to read a long value (release criterion 8).

Change

• Shift+Alt+Right and Shift+Alt+Left widen and narrow the focused cell's column by two digits of its font. Widen Column and Narrow Column in the cell menu do the same and show the keys; the shortcuts window lists them.
• These are GtkTreeView's keys for a focused header. A GTK 4 column view header takes no focus and has no resize key.
• A resized column stops expanding, as in GtkTreeView, and Reset Column Width lets it expand again.

Verified

• Real-key tests through XTEST: both keys resize the focused column and keep the focus; an open cell editor keeps them.

Screenshots

Before	After

Not in this PR

• The keys do not swap in a right-to-left locale, unlike GtkTreeView, so the menu and shortcuts window stay true.