This PR changes the keybinding for the `agent::RejectAll` and
`agent::KeepAll` actions. My initial goal was to free up `cmd-shift-n`
to open a new fresh window again, but that was being used for the reject
all action. Given I had to change the reject all, I figured I had to
change the keep all action, too, to keep them consistent.

Release Notes:

- Agent: Removed keybinding conflict (`cmd-shift-n`) between rejecting
all changes in the agent panel vs. opening a new fresh window.