Update side toolbar menu (#4946)

Side toolbar menu UI updates

## Summary

- Currently the template modal is very hidden. Many users do not find it
- The current icons are quite aleatory 

## Changes

 **What**: 
- Add templates shortcut button
- Add item label in normal size
- Use custom icon

Critical design decisions or edge cases that need attention:
- Sidebar tabs registered using custom icons will have their associated
command registed with an undefined icon (currently only string icons are
accepted, not components). I couldn't see anywhere directly using this
icon, but we should consider autogenerating an icon font so we can use
classes for our custom icons (or locating and updating locations to
support both icon types)

## Screenshots (if applicable)
Normal mode:
<img width="621" height="1034" alt="image"
src="https://github.com/user-attachments/assets/c1d1cee2-004e-4ff8-b3fa-197329b0d2ae"
/>

Small mode:
<img width="176" height="325" alt="image"
src="https://github.com/user-attachments/assets/3824b8f6-bc96-4e62-aece-f0265113d2e3"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-4946-Update-side-toolbar-menu-24d6d73d365081c5b2bdc0ee8b61dc50)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

src/assets/icons/custom/ai-model.svg

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src/assets/icons/custom/node.svg

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src/assets/icons/custom/template.svg

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