Feat: Modify the default style of the agent node anchor #9869 (#10489)

### What problem does this PR solve?

Feat: Modify the default style of the agent node anchor #9869

### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/src/components/canvas/background.tsx

@@ -0,0 +1,13 @@
+import { useIsDarkTheme } from '@/components/theme-provider';
+import { Background } from '@xyflow/react';
+
+export function AgentBackground() {
+  const isDarkTheme = useIsDarkTheme();
+
+  return (
+    <Background
+      color={isDarkTheme ? 'rgba(255,255,255,0.15)' : '#A8A9B3'}
+      bgColor={isDarkTheme ? 'rgba(11, 11, 12, 1)' : 'rgba(0, 0, 0, 0.05)'}
+    />
+  );
+}