feat: add core schema and status enums

backend/src/main/java/com/linhelp/common/api/ApiResponse.java

@@ -0,0 +1,52 @@
+package com.linhelp.common.api;
+
+public class ApiResponse<T> {
+    private int code;
+    private String message;
+    private T data;
+
+    public ApiResponse() {
+    }
+
+    public ApiResponse(int code, String message, T data) {
+        this.code = code;
+        this.message = message;
+        this.data = data;
+    }
+
+    public static <T> ApiResponse<T> ok(T data) {
+        return new ApiResponse<T>(0, "ok", data);
+    }
+
+    public static ApiResponse<Void> ok() {
+        return new ApiResponse<Void>(0, "ok", null);
+    }
+
+    public static ApiResponse<Void> fail(int code, String message) {
+        return new ApiResponse<Void>(code, message, null);
+    }
+
+    public int getCode() {
+        return code;
+    }
+
+    public void setCode(int code) {
+        this.code = code;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+    public T getData() {
+        return data;
+    }
+
+    public void setData(T data) {
+        this.data = data;
+    }
+}