fullRender wrote \x1b[3J\x1b[2J\x1b[H (clear scrollback, then clear
screen). But \x1b[2J pushes on-screen content into scrollback, undoing
the preceding \x1b[3J. Reorder to \x1b[2J\x1b[H\x1b[3J so the screen is
cleared first and scrollback is wiped last.
Map unknown finish_reason values (e.g. "end" from Ollama/LM Studio) to
"stop" instead of throwing, since assistant content is already produced.
fixes#2142
0x08 (BS) was treated as plain backspace alongside 0x7f (DEL). On
Windows Terminal, Backspace sends 0x7f and Ctrl+Backspace sends 0x08,
making ctrl+backspace bindings unreachable.
Now 0x08 matches ctrl+backspace (and ctrl+h, same byte) but not plain
backspace. 0x7f remains plain backspace.
fixes#2139