feat: 搭建后端多租户名片服务

- 初始化 Spring Boot 多模块工程与通用基础能力

- 增加租户、组织、用户、名片、文件、统计等业务模块

- 补充数据库迁移脚本与基础测试

backend/easycard-module-system/pom.xml

@@ -0,0 +1,22 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>com.easycard</groupId>
+    <artifactId>easycard-parent</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>easycard-module-system</artifactId>
+  <name>easycard-module-system</name>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.easycard</groupId>
+      <artifactId>easycard-common</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+  </dependencies>
+</project>

backend/easycard-module-system/src/main/java/com/easycard/module/system/controller/SystemPingController.java

@@ -0,0 +1,29 @@
+package com.easycard.module.system.controller;
+
+import com.easycard.common.api.ApiResponse;
+import com.easycard.common.tenant.TenantContextHolder;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+@RestController
+public class SystemPingController {
+
+    @GetMapping("/api/v1/system/ping")
+    public ApiResponse<Map<String, Object>> ping() {
+        return ApiResponse.success(Map.of(
+                "service", "easycard-backend",
+                "status", "UP"
+        ));
+    }
+
+    @GetMapping("/api/open/ping")
+    public ApiResponse<Map<String, Object>> openPing() {
+        Map<String, Object> payload = new LinkedHashMap<>();
+        payload.put("service", "easycard-open-api");
+        payload.put("tenant", TenantContextHolder.getOptional().orElse(null));
+        return ApiResponse.success(payload);
+    }
+}