feat(search): Optimized search functionality and user interface #3221 (#9535)

### What problem does this PR solve?

feat(search): Optimized search functionality and user interface #3221
### Type of change
- Added similarity threshold adjustment function
- Optimized mind map display logic
- Adjusted search settings interface layout
- Fixed related search and document viewing functions
- Optimized time display and node selection logic

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/pages/agent/canvas/node/dropdown/next-step-dropdown.tsx

@@ -242,7 +242,7 @@ export function InnerNextStepDropdown({
         }}
         onClick={(e) => e.stopPropagation()}
       >
-        <div className="w-[300px] font-semibold bg-white border border-border rounded-md shadow-lg">
+        <div className="w-[300px] font-semibold bg-bg-base border border-border rounded-md shadow-lg">
           <div className="px-3 py-2 border-b border-border">
             <div className="text-sm font-medium">Next Step</div>
           </div>