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/app/(main)/admin/automaticMng/mail/bulk-send/page.tsx

@@ -409,7 +409,7 @@ example2@example.com,김철수,XYZ회사`;
                 {recipients.length > 0 && (
                   <div className="rounded-md border bg-muted p-4">
                     <div className="flex items-center gap-2 text-sm">
-                      <CheckCircle2 className="h-4 w-4 text-green-600" />
+                      <CheckCircle2 className="h-4 w-4 text-emerald-600" />
                       <span className="font-medium">{recipients.length}명의 수신자</span>
                     </div>
                     <p className="mt-1 text-xs text-muted-foreground">