Derive static-cascade color extraction from the shared named-color table

The static-html engine never emitted side-tab for `border-left: 4px solid
purple` (or any named color outside a hardcoded 9-name list) in .html
files: extractStaticColor's regex dropped the color token from border
shorthands, the side defaulted to neutral black, and checkBorders skipped
it. The same declaration in a .css file was flagged by the regex engine,
so the two engines disagreed while both exited cleanly (issue #359).

Build the extraction alternation from the same CSS_NAMED_COLORS table
parseAnyColor resolves against (longest-first, whole-token), so the set of
names the extractor recognizes and the set the parser can resolve cannot
drift apart again. STATIC_NAMED_COLORS shrinks to the one keyword
parseAnyColor deliberately refuses (`transparent` as zero-alpha), since
parseAnyColor already covers every real named color in the table.

New two-column fixture (named-color-borders.html) covers the issue
reproducers: purple shorthand + radius, rebeccapurple (substring-safe
matching), crimson top stripe, bare 3px teal, var() resolving to a named
color, and an inline style attribute — with neutral named colors
(dimgray, gainsboro, black), thin, and uniform borders as pass cases.

Prepared with AI assistance (Claude Code), directed by @pbakaus.

Co-Authored-By: Claude Code <noreply@anthropic.com>

cli/engine/rules/checks.mjs

@@ -5369,6 +5369,7 @@ function checkFirstViewportColumnOverflowDOM() {
 }
 
 export {
+  CSS_NAMED_COLORS,
   checkBorders,
   isEmojiOnlyText,
   checkColors,