### What problem does this PR solve?
Fix: Fixed the issue where the connection lines of placeholder nodes in
the agent canvas could not be displayed #9869
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Hi team, @ZhenhangTung @KevinHuSh @cike8899
About #10384 , I've completed the UI optimization adjustments for the
Agent page according to our previous discussions and the design draft
sketches provided by @Naomi. The main modifications include:
1. Adjusted the style and content of placeholder-node.
2. Adjusted the location of the dropdown (to the right of the
placeholder-node) .
3. Adjusted the tooltip position spacing when the mouse hovers in the
dropdown menu.
4. Hides the thick scroll bar on the dropdown component.
5. Highlight the connection line when dragging to generate a
placeholder-node
<img width="1323" height="509" alt="Image"
src="https://github.com/user-attachments/assets/0d366f7f-477d-4c00-bb58-d5d58b3a745f"
/>
Please review the related code modifications when you have time. Let me
know if further adjustments are needed!
Thanks！
### Type of change
- [x] Other (please describe): UI Enhancement
---------
Co-authored-by: leonlai <leonlai@futurefab.ai>
### What problem does this PR solve?
About issue #10140
In version 0.20.1, we implemented the generation of new node through
mouse drag and drop. If we could create a workflow module like in Coze,
where there is not only a dropdown menu but also an intermediate node
(placeholder node) after the drag and drop is completed, this could
improve the user experience.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
