style: 채번규칙 카드 내부 상하 여백 완전 제거

- CardHeader, CardContent의 py를 0으로 설정
- 좌우 여백(px-3)만 유지
- 최대한 컴팩트한 카드 레이아웃

frontend/components/numbering-rule/NumberingRuleDesigner.tsx

@@ -256,7 +256,7 @@ export const NumberingRuleDesigner: React.FC<NumberingRuleDesignerProps> = ({
                 }`}
                 onClick={() => handleSelectRule(rule)}
               >
-                <CardHeader className="px-3 py-2">
+                <CardHeader className="px-3 py-0">
                   <div className="flex items-start justify-between">
                     <div className="flex-1">
                       <CardTitle className="text-sm font-medium">{rule.ruleName}</CardTitle>
@@ -274,7 +274,7 @@ export const NumberingRuleDesigner: React.FC<NumberingRuleDesignerProps> = ({
                     </Button>
                   </div>
                 </CardHeader>
-                <CardContent className="px-3 pb-2 pt-0">
+                <CardContent className="px-3 py-0">
                   <NumberingRulePreview config={rule} compact />
                 </CardContent>
               </Card>