fix: resolve stale class conflict in Docker build by adding clean and .dockerignore

Dockerfile

@@ -1,30 +1,31 @@
-# 1. ??š®ë±???<3F>ê¼<EFBFBD> (JDK 21)
+# 1. ??<EFBFBD><EFBFBD><EFBFBD>???<3F>꼍 (JDK 21)
 FROM eclipse-temurin:21-jdk-alpine AS builder
 WORKDIR /app
 
-# Gradle ??‘ë<EFBFBD><EFBFBD>?? ???’ª 蹂듭ê¶?
+# Gradle ??<3F>띁?? ???<EFBFBD><EFBFBD> 蹂듭<E8B982>?
 COPY gradlew .
 COPY gradle gradle
 COPY build.gradle settings.gradle ./
 COPY src src
 
-# æ²…ëš°ë¸??ºÂ€??è«???š®ë±?(???’ª????–쇅)
+# 沅뚰<EFBFBD>??<3F>€??<3F>???<3F><><EFBFBD>?(???<EFBFBD><EFBFBD>????<EFBFBD>쇅)
 RUN chmod +x gradlew
 RUN ./gradlew clean build -x test
 
-# 2. ??½ë»¾ ??<3F>ê¼<EFBFBD> (JRE 21)
+# 2. ??<EFBFBD>뻾 ??<3F>꼍 (JRE 21)
 FROM eclipse-temurin:21-jre-alpine
 WORKDIR /app
 
-# ???꾩ã€???¼ì ™ (??“뎅 ??“ì»™)
+# ???꾩<EFBFBD>???<3F>젙 (??<3F>뎅 ??<3F>컙)
 RUN apk add --no-cache tzdata
 ENV TZ=Asia/Seoul
 
-# ??š®ë±??JAR ???”ª 蹂듭ê¶?
+# ??<EFBFBD><EFBFBD><EFBFBD>??JAR ???<EFBFBD><EFBFBD> 蹂듭<E8B982>?
 COPY --from=builder /app/build/libs/*.jar app.jar
 
 # 湲곕???????몄텧
 EXPOSE 8081
 
-# ?Œâ‘¦???€ê¼???½ë»¾ ??JAR ??½ë»¾
+# ?<EFBFBD>⑦???<3F><>???<3F>뻾 ??JAR ??<EFBFBD>뻾
 ENTRYPOINT ["java", "-jar", "app.jar"]
+