feat: add batch operations for forwards, tunnels, and nodes

- Add batch delete, redeploy, and change-tunnel for forwards
- Add batch delete and redeploy for tunnels
- Add batch delete for nodes
- Add multi-select UI with floating toolbar on all three pages
- Create DTOs: BatchDeleteDto, BatchRedeployDto, BatchChangeTunnelDto, BatchOperationResultDto

springboot-backend/src/main/java/com/admin/common/dto/BatchOperationResultDto.java

@@ -0,0 +1,39 @@
+package com.admin.common.dto;
+
+import lombok.Data;
+import java.util.List;
+import java.util.ArrayList;
+
+@Data
+public class BatchOperationResultDto {
+    
+    private int successCount;
+    private int failCount;
+    private List<FailedItem> failedItems = new ArrayList<>();
+    
+    @Data
+    public static class FailedItem {
+        private Long id;
+        private String reason;
+        
+        public FailedItem() {}
+        
+        public FailedItem(Long id, String reason) {
+            this.id = id;
+            this.reason = reason;
+        }
+    }
+    
+    public void addFailedItem(Long id, String reason) {
+        this.failedItems.add(new FailedItem(id, reason));
+        this.failCount++;
+    }
+    
+    public void incrementSuccess() {
+        this.successCount++;
+    }
+    
+    public boolean isAllSuccess() {
+        return failCount == 0;
+    }
+}