feat(fe): standardize empty data state with EmptyStatePlaceholder component and AGENTS.md rule

frontend/src/shared/ui/components/EmptyStatePlaceholder.vue

@@ -0,0 +1,72 @@
+<script setup lang="ts">
+defineProps<{
+  title?: string
+  message?: string
+  icon?: string
+  actionLabel?: string
+}>()
+
+const emit = defineEmits<{ action: [] }>()
+</script>
+
+<template>
+  <div class="ks-empty-state" role="status" aria-label="조회된 데이터 없음">
+    <div class="ks-empty-state__icon">{{ icon ?? '📭' }}</div>
+    <div class="ks-empty-state__title">{{ title ?? '조회된 데이터가 없습니다' }}</div>
+    <p class="ks-empty-state__message">{{ message ?? '검색 조건을 변경하거나 신규 데이터를 생성해 주세요.' }}</p>
+    <button v-if="actionLabel" class="ks-empty-state__action" @click="emit('action')">
+      {{ actionLabel }}
+    </button>
+  </div>
+</template>
+
+<style scoped>
+.ks-empty-state {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  padding: var(--ks-space-4);
+  text-align: center;
+  background: #fff;
+  border: 1px dashed var(--ks-color-neutral-300);
+  border-radius: var(--ks-radius-md);
+  min-height: 220px;
+  flex: 1;
+  width: 100%;
+}
+
+.ks-empty-state__icon {
+  font-size: 32px;
+  line-height: 1;
+  margin-bottom: var(--ks-space-2);
+}
+
+.ks-empty-state__title {
+  font-size: var(--ks-font-body);
+  font-weight: 700;
+  color: var(--ks-color-neutral-800);
+  margin-bottom: var(--ks-space-1);
+}
+
+.ks-empty-state__message {
+  font-size: var(--ks-font-caption);
+  color: var(--ks-color-neutral-600);
+  margin: 0;
+  max-width: 360px;
+}
+
+.ks-empty-state__action {
+  margin-top: var(--ks-space-3);
+  padding: 4px 12px;
+  font-size: var(--ks-font-caption);
+  background: var(--ks-color-action);
+  color: #fff;
+  border: none;
+  border-radius: var(--ks-radius-sm);
+  cursor: pointer;
+}
+.ks-empty-state__action:hover {
+  background: var(--ks-color-action-hover);
+}
+</style>

frontend/src/shared/ui/components/index.ts

@@ -1,4 +1,5 @@
 export { default as SkeletonLoader } from './SkeletonLoader.vue'
+export { default as EmptyStatePlaceholder } from './EmptyStatePlaceholder.vue'
 export { default as KsButton } from './KsButton.vue'
 export { default as KsTextField } from './KsTextField.vue'
 export { default as KsTextArea } from './KsTextArea.vue'