redraw.c: the CSS3 text-decoration longhands were parsed/cascaded by
libcss but dropped at paint. Now html_redraw_text_decoration reads
css_computed_text_decoration_color (override the line colour when set;
CURRENT_COLOR keeps text colour) and css_computed_text_decoration_style,
threading the style into the inline/block painters. New helper
html_redraw_decoration_run emits solid/double/dotted/dashed/wavy via
segmented plot->line calls (macos9 plotter line op is solid-only, so
patterning is done here — no plotter/pen-state risk). Wavy is a V1
1px-zigzag approximation. Consumer-side only: no libcss/preprocessor
changes, no new .c files. PPC C89 clean (0 errors, redraw.c full parse).