Previous approach using Place() for full-screen bg and WarmRowStyle wrapper
failed because inner ANSI resets (\x1b[m) kill outer Background() styles.
New approach: every styled segment carries its own Background() via theme.Bg()
and theme.WBg() helpers. Per-line Place() fills trailing whitespace. This
ensures cream bg (#fdf6ef) on every pixel of every line, and warm bg (#f8f0e6)
consistently across the cursor row.
Also fixes bottom bar overflow on narrow terminals with adaptive keybindings.
noah
ed25ffa533