sl0p: first keystroke replaces the old tab name when renaming

Entering RenameTab left the existing name in place and appended to it, so
renaming a tab meant clearing it by hand first. The first printable keystroke
now REPLACES it, the way a text field with its contents selected behaves.

Armed when a client enters RenameTab and disarmed when it leaves, so a
keystroke that arrives later cannot wipe a name the user was not editing.
Backspace and delete deliberately do NOT replace: reaching for them means
editing the existing name, not discarding it.

The flag is taken out of the set BEFORE borrowing the active tab, since
get_active_tab_mut borrows self mutably and every branch consumes the flag
anyway.

Applies to renames from any entry point - the keybind and the sl0pstatus
double-click-a-tab both go through Screen::change_mode.

Pane rename is deliberately left alone for now; say the word and it can get
the same treatment.

Baselines held: zellij-server 1441/30.

0 files changed, 0 insertions, 0 deletions