feat(ui): P4-4 별점 공통화 + 로그인 모달 접근성 (#281+#283)

#281 (리뷰/메모 UI):
- Stars 컴포넌트 신규 (lib 분리 가능한 공통 별점) — 0.5 단위 절반 채우기 시각 구분
- ReviewSection/MemoSection의 StarDisplay 제거 → 공통 Stars 사용 (시각 일관성)
- StarSelector: role='radiogroup'/role='radio' + aria-checked, 44×44px 터치 영역,
  반쪽 별 '⯨' 표시로 시각 차별화
- ReviewSection/MemoSection: API 실패 try/catch + alert 사용자 피드백
- MyReviewsList: Math.round 별점 → Stars 0.5단위 정확 렌더

#283 (로그인 메뉴):
- LoginMenu: useEscapeKey + useFocusTrap + useBodyScrollLock 적용
- role='dialog' / aria-modal / aria-labelledby / aria-label='로그인 창 닫기'
- onError 콘솔만 → 인라인 role='alert' 메시지로 사용자 피드백
- max-w-xs → max-w-sm (위젯 260px + 패딩 24px = 308px 안전 수용)

후속 분리:
- #343 (next/image + ARIA Tabs + Stars 테스트)
- #344 (z-index 토큰 + i18n)

Refs: #281 #283

frontend/src/components/MemoSection.tsx

@@ -5,11 +5,13 @@ import { api } from "@/lib/api";
 import type { Memo } from "@/lib/api";
 import { useAuth } from "@/lib/auth-context";
 import Icon from "@/components/Icon";
+import Stars from "@/components/Stars";
 
 interface MemoSectionProps {
   restaurantId: string;
 }
 
+// #281 — ReviewSection의 StarSelector와 동일 UX (0.5 단위 + 44px 터치 + ARIA radiogroup)
 function StarSelector({
   value,
   onChange,
@@ -18,38 +20,32 @@ function StarSelector({
   onChange: (v: number) => void;
 }) {
   return (
-    <div className="flex items-center gap-1">
+    <div role="radiogroup" aria-label="별점 선택" className="flex items-center gap-0.5">
       <span className="text-xs text-gray-500 mr-1">별점:</span>
-      {[0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5].map((v) => (
-        <button
-          key={v}
-          type="button"
-          onClick={() => onChange(v)}
-          className={`w-6 h-6 text-xs rounded border ${
-            value === v
-              ? "bg-yellow-500 text-white border-yellow-600"
-              : "bg-white text-gray-600 border-gray-300 hover:border-yellow-400"
-          }`}
-        >
-          {v}
-        </button>
-      ))}
+      {[1, 2, 3, 4, 5].map((v) => {
+        const nextVal = value === v ? v - 0.5 : v;
+        return (
+          <button
+            key={v}
+            type="button"
+            role="radio"
+            aria-checked={value >= v - 0.5 && value <= v}
+            aria-label={`${nextVal}점`}
+            onClick={() => onChange(nextVal)}
+            className="min-w-[44px] min-h-[44px] flex items-center justify-center touch-manipulation"
+            title={`${nextVal}점`}
+          >
+            <span className={`text-xl ${v <= value ? "text-yellow-500" : v - 0.5 === value ? "text-yellow-400" : "text-gray-300"}`}>
+              {v <= value ? "★" : v - 0.5 === value ? "⯨" : "☆"}
+            </span>
+          </button>
+        );
+      })}
+      {value > 0 && <span className="text-xs text-yellow-600 font-medium ml-1">{value}</span>}
     </div>
   );
 }
 
-function StarDisplay({ rating }: { rating: number }) {
-  const stars = [];
-  for (let i = 1; i <= 5; i++) {
-    stars.push(
-      <span key={i} className={rating >= i - 0.5 ? "text-yellow-500" : "text-gray-300"}>
-        ★
-      </span>
-    );
-  }
-  return <span className="text-sm">{stars}</span>;
-}
-
 export default function MemoSection({ restaurantId }: MemoSectionProps) {
   const { user } = useAuth();
   const [memo, setMemo] = useState<Memo | null>(null);
@@ -104,6 +100,9 @@ export default function MemoSection({ restaurantId }: MemoSectionProps) {
       setMemo(saved);
       setShowForm(false);
       setEditing(false);
+    } catch (err) {
+      // #281 — 사용자 피드백
+      alert(`메모 저장 실패: ${err instanceof Error ? err.message : String(err)}`);
     } finally {
       setSubmitting(false);
     }
@@ -111,8 +110,12 @@ export default function MemoSection({ restaurantId }: MemoSectionProps) {
 
   const handleDelete = async () => {
     if (!confirm("메모를 삭제하시겠습니까?")) return;
-    await api.deleteMemo(restaurantId);
-    setMemo(null);
+    try {
+      await api.deleteMemo(restaurantId);
+      setMemo(null);
+    } catch (err) {
+      alert(`메모 삭제 실패: ${err instanceof Error ? err.message : String(err)}`);
+    }
   };
 
   return (
@@ -167,7 +170,7 @@ export default function MemoSection({ restaurantId }: MemoSectionProps) {
       ) : memo ? (
         <div className="border border-brand-200 rounded-lg p-3 bg-brand-50/30">
           <div className="flex items-center gap-2 mb-1">
-            {memo.rating && <StarDisplay rating={memo.rating} />}
+            {memo.rating && <Stars rating={memo.rating} />}
             {memo.visited_at && (
               <span className="text-xs text-gray-400">방문일: {memo.visited_at}</span>
             )}