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/admin/ExternalDbConnectionModal.tsx

@@ -484,7 +484,7 @@ export const ExternalDbConnectionModal: React.FC<ExternalDbConnectionModalProps>
                 <div
                   className={`rounded-md border p-3 text-sm ${
                     testResult.success
-                      ? "border-green-200 bg-green-50 text-green-800"
+                      ? "border-emerald-200 bg-emerald-50 text-emerald-800"
                       : "border-destructive/20 bg-destructive/10 text-red-800"
                   }`}
                 >
@@ -527,7 +527,7 @@ export const ExternalDbConnectionModal: React.FC<ExternalDbConnectionModalProps>
             </Button>
 
             {showAdvanced && (
-              <div className="space-y-4 border-l-2 border-gray-200 pl-6">
+              <div className="space-y-4 border-l-2 border-border pl-6">
                 <div className="grid grid-cols-3 gap-4">
                   <div>
                     <Label htmlFor="connection_timeout">연결 타임아웃 (초)</Label>