refactor: 전체 프론트엔드 하드코딩 색상 → CSS 변수 일괄 치환

447+ 파일, 4500+ 줄 변경:
- gray-* → border/bg-muted/text-foreground/text-muted-foreground
- blue-* → primary/ring
- red-* → destructive
- green-* → emerald (일관성)
- indigo-* → primary
- yellow/orange → amber (통일)
- dark mode 변형도 시맨틱 토큰으로 변환

Made-with: Cursor

frontend/components/unified/UnifiedSelect.tsx

@@ -801,7 +801,7 @@ export const UnifiedSelect = forwardRef<HTMLDivElement, UnifiedSelectProps>((pro
           className="flex-shrink-0 text-sm font-medium"
         >
           {label}
-          {required && <span className="ml-0.5 text-orange-500">*</span>}
+          {required && <span className="ml-0.5 text-amber-500">*</span>}
         </Label>
       )}
       <div className="min-h-0 flex-1">{renderSelect()}</div>