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/layout/MainSidebar.tsx

@@ -79,7 +79,7 @@ export function MainSidebar({ menuList, expandedMenus, onMenuClick, className =
   return (
     <nav className={cn("space-y-1 overflow-y-auto", className)}>
       {menuList.length === 0 ? (
-        <div className="text-sm text-gray-500">{MESSAGES.NO_MENUS}</div>
+        <div className="text-sm text-muted-foreground">{MESSAGES.NO_MENUS}</div>
       ) : (
         menuList.map((menu) => renderMenuItem(menu))
       )}

frontend/components/layout/ProfileModal.tsx

@@ -48,7 +48,7 @@ function AlertModal({ isOpen, onClose, title, message, type = "info" }: AlertMod
   const getTypeColor = () => {
     switch (type) {
       case "success":
-        return "text-green-600";
+        return "text-emerald-600";
       case "error":
         return "text-destructive";
       default: