🪟 fix: Auto-fetch agents to fill Viewport in Marketplace Scroll

[sbruel]

Summary

Infinite scrolling has agents marketplace has a few issues:

• if the viewport is tall enough by default to show more than 6 items (and there is no scrollbar), there is no way to get more items to show
• when the window is resized to become bigger, and could potentially show more agents, the agents are not shown
• when switching between category tabs before scrolling, he infinite scroll does not work on the other categories.

This PR fixes all these issues. Check the videos for before / after.

Before

2025-09-12-infinite-scroll-before-s.mov

After

2025-09-12-infinite-scroll-after-s.mov

Change Type

• Bug fix (non-breaking change which fixes an issue)

Testing

Follow the 3 different scenarios described in the summary or in the video.

Checklist

Please delete any irrelevant options.

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes