Skip CRLF normalization on alt screen

[devsunb]

Summary

Skip bare-LF -> CRLF normalization while the terminal is on the alternate screen.

Why

Emacs PTYs lack ONLCR, so the module inserts \r before each bare \n - correct for line-oriented output on the primary screen. But alt-screen apps (tmux, vim, less) emit VT-correct LF (cursor down, column preserved); normalizing those to \r\n corrupts their layout.

Fix

Skip the conversion when the active screen is the alternate one:

if (term.terminal.screens.active_key == .alternate) {
    term.vtWrite(raw);
    ...
}

Detection via screens.active_key covers all three alt-screen entry modes (DECSET 47 / 1047 / 1049) uniformly. last_input_was_cr is still maintained so a CRLF pair split across writes isn't mis-normalized into \r\r\n.

Demo

Before

before.mp4

After

after.mp4

[dakra]

@emil-e you have a quick look as well but lgtm