Repoint session.newWindow (⌘⇧N) from the compact new-session pop-out to
openNewWindow(), which opens a full peer instance via the new openWindow
bridge, and add a "New Window" entry to the ⌘K palette (shown with its
hotkey hint, gated on canOpenNewWindow()). Relabel the action "New window".
Drops the retired openNewSessionWindow bridge and the vestigial
isNewSessionWindow()/new=1 flag; renames the shared opener helper.
a90ca7fe34