refactor: 重构项目结构，迁移后端至 mengyastore-backend-go，新增 Java 后端、前端功能更新及部署文档

mengyastore-backend-go/mengyastore-backend-java/build.gradle

@@ -0,0 +1,39 @@
+plugins {
+    id 'java'
+    id 'org.springframework.boot' version '4.0.4'
+    id 'io.spring.dependency-management' version '1.1.7'
+}
+
+group = 'com.smyhub.store'
+version = '0.0.1-SNAPSHOT'
+description = 'mengyastore-backend-java'
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(17)
+    }
+}
+
+configurations {
+    compileOnly {
+        extendsFrom annotationProcessor
+    }
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter'
+    compileOnly 'org.projectlombok:lombok'
+    developmentOnly 'org.springframework.boot:spring-boot-devtools'
+    developmentOnly 'org.springframework.boot:spring-boot-docker-compose'
+    annotationProcessor 'org.projectlombok:lombok'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
+}