refactor: replace hardcoded hex values with Tailwind semantic tokens

3,200+ hardcoded color values replaced with CSS variable-backed
Tailwind classes (bg-card, text-foreground, border-border, etc.).
Enables light mode via CSS variable swap. Only syntax highlighting
colors and intentional one-offs remain hardcoded (~15 values).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/common/StarRating.tsx

@@ -48,14 +48,14 @@ export function StarRating({
               sizeClasses[size],
               star <= value
                 ? 'fill-yellow-400 text-yellow-400'
-                : 'fill-none text-[#848b9b]',
+                : 'fill-none text-muted-foreground',
               !readonly && 'hover:text-yellow-300'
             )}
           />
         </button>
       ))}
       {showCount && (
-        <span className="ml-1 text-sm text-[#848b9b]">
+        <span className="ml-1 text-sm text-muted-foreground">
           ({value}/5)
         </span>
       )}