fix: 统一弹框组件 — ModalOverlay对齐EditInstanceDialog行为

- ModalOverlay移除遮罩层onClick(不响应外部点击关闭)
- 移除body.style.overflow=hidden(修复白条问题)
- max-h从90vh改为85vh(与EditInstanceDialog一致)
- 10个页面手写fixed弹框替换为ModalOverlay组件
- InstanceGroupPage/WorkflowPage/UsersPage/RedisDetailPage/TicketsPage已替换
- dialog.tsx添加onPointerDownOutside/onInteractOutside阻止外部点击
- index.css添加body[data-scroll-locked]覆盖Radix滚动锁定
- Layout.tsx main添加relative定位上下文

frontend/src/components/ModalOverlay.tsx

@@ -0,0 +1,40 @@
+import { useEffect, useCallback } from 'react';
+
+interface ModalOverlayProps {
+  open: boolean;
+  onClose: () => void;
+  width?: string;
+  className?: string;
+  children: React.ReactNode;
+}
+
+export function ModalOverlay({ open, onClose, width = 'max-w-lg', className = '', children }: ModalOverlayProps) {
+  const handleKeyDown = useCallback(
+    (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose();
+    },
+    [onClose],
+  );
+
+  useEffect(() => {
+    if (open) {
+      document.addEventListener('keydown', handleKeyDown);
+    }
+    return () => {
+      document.removeEventListener('keydown', handleKeyDown);
+    };
+  }, [open, handleKeyDown]);
+
+  if (!open) return null;
+
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/50 backdrop-blur-sm">
+      <div
+        className={`bg-[var(--dg-bg-secondary)] rounded-xl shadow-2xl w-full ${width} max-h-[85vh] overflow-y-auto ${className}`}
+        onClick={(e) => e.stopPropagation()}
+      >
+        {children}
+      </div>
+    </div>
+  );
+}