fix(system/message): avoid bean-name collision with existing work/message module

Existing com.zioinfo.kintex.work.message.{MessageController,MessageService,MessageMapper}
share default bean names with the new system/message beans, causing
ConflictingBeanDefinitionException at startup (health-check fail -> rollback).
- rename mapper interface MessageMapper -> SysMessageMapper (MyBatis bean name can't
  be overridden by annotation value)
- explicit bean names: @RestController("sysMessageController"), @Service("sysMessageService")
No request-path change (new: /api/admin/messages, /api/messages/{code}/render).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/backend/src/main/java/com/zioinfo/kintex/system/message/MessageController.java

@@ -21,7 +21,7 @@ import java.util.Map;
  *  - DELETE /api/admin/messages/{code}   삭제(locale 옵션)            [ADMIN]
  *  - POST /api/messages/{code}/render    {params:{...}} → 치환 문자열  [인증]
  */
-@RestController
+@RestController("sysMessageController")
 public class MessageController {
 
     private final MessageService service;

src/backend/src/main/java/com/zioinfo/kintex/system/message/MessageService.java

@@ -13,7 +13,7 @@ import java.util.regex.Pattern;
  * <p>렌더: template 의 {key} 를 params[key] 로 치환한다. 파라미터가 없으면 원본 {key} 를 유지하고(안전),
  * 값이 null 이면 빈 문자열로 치환한다. 알림/이메일(W10)·통지에서 {@link #render}/{@link #renderTemplate} 재사용.
  */
-@Service
+@Service("sysMessageService")
 public class MessageService {
 
     /** {key} — 영문/숫자/밑줄/점만 허용(중괄호 오탐 방지). */
@@ -21,9 +21,9 @@ public class MessageService {
     private static final String DEFAULT_TENANT = "KINTEX";
     private static final String DEFAULT_LOCALE = "ko";
 
-    private final MessageMapper mapper;
+    private final SysMessageMapper mapper;
 
-    public MessageService(MessageMapper mapper) {
+    public MessageService(SysMessageMapper mapper) {
         this.mapper = mapper;
     }
 

src/backend/src/main/java/com/zioinfo/kintex/system/message/SysMessageMapper.java

@@ -7,9 +7,10 @@ import java.util.Map;
 
 /**
  * 메시지 템플릿 매퍼(sys_message). 필터는 null-safe(값이 없으면 조건 무시) — <script> 미사용.
+ * <p>클래스명 Sys* 접두 — 기존 {@code work.message.MessageMapper} 와 MyBatis 매퍼 빈명 충돌 회피.
  */
 @Mapper
-public interface MessageMapper {
+public interface SysMessageMapper {
 
     @Select("SELECT msg_code AS \"msgCode\", locale, category, title, template, use_yn AS \"useYn\", "
             + "to_char(updated_at,'YYYY-MM-DD\"T\"HH24:MI:SS') AS \"updatedAt\" FROM sys_message "