What
Adds the standard readline/emacs Ctrl+P (previous) / Ctrl+N (next) history bindings. Den only bound Up/Down arrows; Ctrl+P/N are constant muscle memory for bash/zsh users.
Both wire to the existing historyPrevious / historyNext, so they mirror the arrows exactly (including completion-state clearing).
Verification
zig buildclean.- PTY test: after
echo ALPHAthenecho BETA, Ctrl+P recallsecho BETAand running it printsBETA.
8-line addition to the control-key dispatch in src/utils/terminal/line_editor.zig; no API changes.