## Context
Sets up infinite loading for notebooks with the `InfiniteListDefault`
component
Also adds the notebook and chats count on the explorer home nav
<img width="275" height="137" alt="image"
src="https://github.com/user-attachments/assets/c3f16e8f-f520-4107-a188-43b1abcca043"
/>
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Explorer navigation now displays accurate notebook and chat counts.
* Notebook lists support infinite scrolling, loading indicators, and
improved active-state styling.
* Notebook navigation remains available as additional items load.
* **Bug Fixes**
* Corrected default markdown cell formatting by removing unintended
leading spaces from headings and notes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Charis <26616127+charislam@users.noreply.github.com>
