'Keep file' shortcut 'k' conflicts with Vim navigation in merge conflict menu

When resolving non-textual merge conflicts (e.g. file modified on one side, deleted on the other), the "Keep file" option has shortcut key 'k'. This conflicts with vim-style navigation where 'k' moves up in the menu, leading to accidental selection when users just want to navigate upward.

Possible solution, PR #5366 : Change the shortcut to 'r' (for "retain") to avoid this conflict.

Inspect the merge conflict menu implementation and its tests, focusing on the "Keep file" action and its current 'k' shortcut. Review the possible solution in PR #5366, then change the shortcut to 'r' and verify that Vim-style upward navigation with 'k' no longer selects the action.

Written by the indexing model from the issue text.