feat(chat): 캐릭터 리스트, 추가/수정 폼, 배너

- response의 데이터 구조에 맞춰서 코드 수정

src/api/character.js

@@ -19,6 +19,14 @@ async function getCharacter(id) {
   return Vue.axios.get(`/admin/chat/character/${id}`)
 }
 
+// 내부 헬퍼: 빈 문자열을 null로 변환
+function toNullIfBlank(value) {
+  if (typeof value === 'string') {
+    return value.trim() === '' ? null : value;
+  }
+  return value === '' ? null : value;
+}
+
 // 캐릭터 등록
 async function createCharacter(characterData) {
   const formData = new FormData()
@@ -28,18 +36,18 @@ async function createCharacter(characterData) {
 
   // 나머지 데이터는 JSON 문자열로 변환하여 request 필드에 추가
   const requestData = {
-    name: characterData.name,
-    systemPrompt: characterData.systemPrompt,
-    description: characterData.description,
-    age: characterData.age,
-    gender: characterData.gender,
-    mbti: characterData.mbti,
-    characterType: characterData.type,
-    originalTitle: characterData.originalTitle,
-    originalLink: characterData.originalLink,
-    speechPattern: characterData.speechPattern,
-    speechStyle: characterData.conversationStyle,
-    appearance: characterData.appearance,
+    name: toNullIfBlank(characterData.name),
+    systemPrompt: toNullIfBlank(characterData.systemPrompt),
+    description: toNullIfBlank(characterData.description),
+    age: toNullIfBlank(characterData.age),
+    gender: toNullIfBlank(characterData.gender),
+    mbti: toNullIfBlank(characterData.mbti),
+    characterType: toNullIfBlank(characterData.type),
+    originalTitle: toNullIfBlank(characterData.originalTitle),
+    originalLink: toNullIfBlank(characterData.originalLink),
+    speechPattern: toNullIfBlank(characterData.speechPattern),
+    speechStyle: toNullIfBlank(characterData.speechStyle),
+    appearance: toNullIfBlank(characterData.appearance),
     tags: characterData.tags || [],
     hobbies: characterData.hobbies || [],
     values: characterData.values || [],
@@ -66,9 +74,18 @@ async function updateCharacter(characterData, image = null) {
   // 이미지가 있는 경우에만 FormData에 추가
   if (image) formData.append('image', image)
 
-  // 변경된 데이터만 JSON 문자열로 변환하여 request 필드에 추가
+  // 변경된 데이터만 JSON 문자열로 변환하여 request 필드에 추가 ('' -> null 변환)
   // characterData는 이미 변경된 필드만 포함하고 있음
-  formData.append('request', JSON.stringify(characterData))
+  const processed = {}
+  Object.keys(characterData).forEach(key => {
+    const value = characterData[key]
+    if (typeof value === 'string' || value === '') {
+      processed[key] = toNullIfBlank(value)
+    } else {
+      processed[key] = value
+    }
+  })
+  formData.append('request', JSON.stringify(processed))
 
   return Vue.axios.put(`/admin/chat/character/update`, formData, {
     headers: {