feat: P5-2 작은 후속 (#338+#320+#340+#333)

#338: /api/version 신규
- HealthController에 @Value 빌드 정보 + GET /api/version 추가
- SecurityConfig.permitAll에 /api/version 추가
- application.yml app.build.version/commit (env APP_VERSION/APP_COMMIT)
- 부수: SecurityConfig에서 /api/daemon/config permitAll 제거 (이미 admin-only)

#320: findRegionFromCoords 거리 보정
- 유클리드 거리 → cos(lat) 가중치(equirectangular approx)로 위경도 실거리 보정
- 위도가 큰 지역(부산↔서울)에서 city 추정 정확도 향상

#340: MapView 마커/범례 ARIA
- 클러스터 마커: role=button + aria-label
- 개별 식당 마커: role=button + aria-label (name + 폐업 여부)
- 채널 범례: role=region + aria-label, 색상 점은 aria-hidden

#333: ChannelController 캐시 세분화
- cache.flush() 전체 무효화 → cache.del(makeKey("channels"))로 채널 키만 evict
- 다른 모듈(restaurants/search) 캐시 hit율 보존

후속: deploy.sh에 APP_VERSION/APP_COMMIT env 주입은 별도 (현재 dev/unknown 응답)

Refs: #338 #320 #340 #333

frontend/src/components/MapView.tsx

@@ -209,6 +209,8 @@ function MapContent({ restaurants, selected, onSelectRestaurant, flyTo, activeCh
               zIndex={100}
             >
               <div
+                role="button"
+                aria-label={`${point_count}개 식당이 모인 클러스터, 클릭하면 확대됩니다`}
                 style={{
                   width: size,
                   height: size,
@@ -246,7 +248,10 @@ function MapContent({ restaurants, selected, onSelectRestaurant, flyTo, activeCh
             onClick={() => handleMarkerClick(r)}
             zIndex={isSelected ? 1000 : 1}
           >
-            <div style={{ display: "flex", flexDirection: "column", alignItems: "center", transition: "transform 0.2s ease", transform: isSelected ? "scale(1.15)" : "scale(1)", opacity: isClosed ? 0.5 : 1 }}>
+            <div
+              role="button"
+              aria-label={`${r.name}${isClosed ? ' (폐업)' : ''}, 클릭하면 상세 정보가 표시됩니다`}
+              style={{ display: "flex", flexDirection: "column", alignItems: "center", transition: "transform 0.2s ease", transform: isSelected ? "scale(1.15)" : "scale(1)", opacity: isClosed ? 0.5 : 1 }}>
               <div
                 style={{
                   padding: "4px 8px",
@@ -389,10 +394,15 @@ export default function MapView({ restaurants, selected, onSelectRestaurant, onB
         </button>
       )}
       {channelNames.length > 0 && (
-        <div className="absolute bottom-2 left-2 bg-surface/90 backdrop-blur-sm rounded-lg shadow px-2.5 py-1.5 flex flex-wrap gap-x-3 gap-y-1 text-[11px] z-10">
+        <div
+          role="region"
+          aria-label="채널 범례"
+          className="absolute bottom-2 left-2 bg-surface/90 backdrop-blur-sm rounded-lg shadow px-2.5 py-1.5 flex flex-wrap gap-x-3 gap-y-1 text-[11px] z-10"
+        >
           {channelNames.map((ch) => (
             <div key={ch} className="flex items-center gap-1">
               <span
+                aria-hidden="true"
                 className="inline-block w-2.5 h-2.5 rounded-full border"
                 style={{ backgroundColor: channelColors[ch].border, borderColor: channelColors[ch].border }}
               />