Fix radius var fallback detection (#687)

Strip closing var() parentheses before resolving fallback radius tokens, preserving on-scale values and actionable ignore values.

AI-assisted change: implemented with Codex under @pbakaus direction.

cli/engine/design-system.mjs

@@ -995,7 +995,9 @@ function extractRadiusTokens(value) {
   return String(value || '')
     .replace(/\s*\/\s*/g, ' ')
     .split(/\s+/)
-    .map(token => token.trim())
+    // var() fallbacks leave the closing parenthesis on the final token. Strip
+    // it before length resolution so `8px)` is not treated as unitless 8rem.
+    .map(token => token.trim().replace(/\)+$/, ''))
     .filter(Boolean);
 }