terminfo: declare Smulx and Su for the new underline extensions
Verified against real terminfo databases rather than assumed
(infocmp -x): Smulx=\E[4:%p1%dm is byte-identical across
tmux-256color/kitty/alacritty/wezterm/contour/foot (%p1 takes the
style number 0-5 directly, no offset), and boolean Su is what
st/st-256color declare for the special-underline-color extension --
no parameterized string capability for it exists in practice, since
SGR 58/59's own syntax is already fixed and universal. Setulc/Setulc1
were checked for and don't actually exist in any real terminfo
database inspected, so they're deliberately not declared.
Also records the whole undercurl/extended-underline feature in
ROADMAP.md, matching the file's existing narrative-detail convention.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011F9RnepbqPL8bDBudDwt71