refactor: 根包由 com.bestsch.bschclassmanage 重命名为 com.yunhai.bschclassmanage

- git mv src/main/java/com/bestsch/bschclassmanage -> src/main/java/com/yunhai/bschclassmanage
- 255 个 Java 文件的 package/import 同步替换为 com.yunhai.bschclassmanage
- pom.xml 项目 groupId 设为 com.yunhai（与外部依赖 com.bestsch:bsch-* 无关，未改动）
- IDE 缓存 workspace.xml 路径同步更新（外部依赖坐标 com.bestsch:bsch-* 保持不动）

src/main/java/com/yunhai/bschclassmanage/controller/Handler/ValidationExceptionHandler.java

@@ -0,0 +1,33 @@
+package com.yunhai.bschclassmanage.controller.Handler;
+
+import com.yunhai.platform.utils.exception.ErrorCode;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+import java.util.*;
+
+@RestControllerAdvice
+public class ValidationExceptionHandler {
+
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    public ResponseEntity<Map<String, Object>> handleValidationExceptions(MethodArgumentNotValidException ex) {
+        List<String> msgList = new ArrayList<>();
+        ex.getBindingResult().getAllErrors().forEach(error -> {
+            String errorMessage = error.getDefaultMessage();
+            msgList.add(errorMessage);
+        });
+
+        Map<String, Object> response = new LinkedHashMap<>();
+        response.put("code", ErrorCode.ERROR.getCode());
+        response.put("msg", String.join(";", msgList));
+        response.put("data", null);
+        response.put("timeNow", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
+
+        return new ResponseEntity(response, HttpStatus.BAD_REQUEST);
+    }
+}