Enhance Dockerfile and README: Configure Maven to use Alibaba Cloud mirror for faster dependency downloads and update troubleshooting instructions for Maven dependency issues.

docker/Dockerfile

@@ -15,15 +15,36 @@ RUN npm run build
 FROM maven:3.8-eclipse-temurin-8-alpine AS backend-builder
 WORKDIR /app
 
+# 配置 Maven 使用阿里云镜像（加速下载，解决网络问题）
+RUN mkdir -p /root/.m2 && \
+    cat > /root/.m2/settings.xml << 'EOF'
+<?xml version="1.0" encoding="UTF-8"?>
+<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
+          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
+  <mirrors>
+    <mirror>
+      <id>aliyunmaven</id>
+      <mirrorOf>central</mirrorOf>
+      <name>阿里云公共仓库</name>
+      <url>https://maven.aliyun.com/repository/public</url>
+    </mirror>
+  </mirrors>
+</settings>
+EOF
+
 # 复制后端源码
 COPY backend/pom.xml ./
-RUN mvn dependency:go-offline -B
+# 验证并下载依赖（如果失败会自动重试）
+RUN mvn dependency:resolve -B -s /root/.m2/settings.xml || \
+    (echo "依赖下载失败，重试中..." && sleep 2 && mvn dependency:resolve -B -s /root/.m2/settings.xml)
 
 COPY backend/ ./
 # 从阶段1 复制前端构建产物到 Spring Boot 静态目录
 COPY --from=frontend-builder /app/frontend/dist ./src/main/resources/static
 
-RUN mvn package -DskipTests -B
+# 构建项目（跳过测试）
+RUN mvn clean package -DskipTests -B -s /root/.m2/settings.xml
 
 # 阶段3：运行镜像
 FROM eclipse-temurin:8-jre-alpine