fix(admin-service): 添加uploads目录的volume持久化配置

问题：admin-service重新部署后，上传的APK文件会丢失
原因：主docker-compose.yml中admin-service未配置volume挂载，
      导致容器重建时/app/uploads目录数据丢失

修复：
- 添加admin_uploads_data volume挂载到/app/uploads
- 添加UPLOAD_DIR环境变量
- 在volumes部分声明admin_uploads_data

影响范围：仅影响admin-service的文件存储持久化

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/docker-compose.yml

@@ -644,6 +644,10 @@ services:
       - KAFKA_CONSUMER_GROUP=admin-service-user-sync
       # CDC Consumer (Debezium)
       - KAFKA_CDC_CONSUMER_GROUP=admin-service-cdc
+      # File Storage
+      - UPLOAD_DIR=/app/uploads
+    volumes:
+      - admin_uploads_data:/app/uploads
     depends_on:
       postgres:
         condition: service_healthy
@@ -764,6 +768,8 @@ volumes:
     driver: local
   redis_data:
     driver: local
+  admin_uploads_data:
+    driver: local
 
 # ===========================================================================
 # Networks