refactor: 重构安全架构，提取通用安全模块到common-security

- 将JwtAuthenticationFilter、JwtUtil、JwtProperties从auth服务移至common-security模块
- 新增common-security通用安全模块，提供JWT认证、权限验证等核心安全功能
- 重命名SecurityConfiguration为AuthSecurityConfiguration，使用common-security的filter
- 新增JacksonConfiguration配置类，统一JSON序列化配置
- 新增头像更新功能AvatarUpdateRequestDTO
- 移除冗余的UserLoginResponseDTO类
- 更新各服务模块的依赖配置以引入common-security模块
- 新增README.md项目说明文档

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

aioj-backend-common/aioj-backend-common-security/.flattened-pom.xml

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>cn.meowrain.aioj</groupId>
+    <artifactId>aioj-backend-common</artifactId>
+    <version>1.0.0</version>
+  </parent>
+  <artifactId>aioj-backend-common-security</artifactId>
+  <version>1.0.0</version>
+  <description>AIOJ 公共安全模块 - JWT 认证和 Spring Security 配置</description>
+  <licenses>
+    <license>
+      <name>Apache License, Version 2.0</name>
+      <url>https://www.apache.org/licenses/LICENSE-2.0</url>
+    </license>
+  </licenses>
+  <dependencies>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-security</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-web</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-configuration-processor</artifactId>
+      <optional>true</optional>
+    </dependency>
+    <dependency>
+      <groupId>io.jsonwebtoken</groupId>
+      <artifactId>jjwt-api</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>io.jsonwebtoken</groupId>
+      <artifactId>jjwt-impl</artifactId>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>io.jsonwebtoken</groupId>
+      <artifactId>jjwt-jackson</artifactId>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.projectlombok</groupId>
+      <artifactId>lombok</artifactId>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>cn.meowrain.aioj</groupId>
+      <artifactId>aioj-backend-common-core</artifactId>
+    </dependency>
+  </dependencies>
+</project>