UI color updates & tweaks (#6381)

## Summary

Small updates to the UI to make it more visually distinct from the graph
nodes and improving the login button

## Changes

- **What**: 
  - Improve theme support with dynamic colors
  - Standardize surface colors/borders
  - Add shadows to all floating UI elements
  - Change side toolbar to be docked by default
  - Decrease side toolbar width
  - Change login button to icon only
  - Update C button to be more distinctive

## Review Focus

- Theme tokens, I am not sure what the overall plan for how these tokens
will be supported for custom user palettes. I've implemented a method
where default variables are chosen that look nice over all existing
themes, but they can be overridden.

## Screenshots

Dark theme updated color
<img width="958" height="615" alt="image"
src="https://github.com/user-attachments/assets/a2c540cf-6c05-4ad3-996b-8b7b80df8d2d"
/>

Themed & updated menu button (active vs hover vs default)
<img width="58" height="338" alt="github"
src="https://github.com/user-attachments/assets/90244ee2-d5ee-4b26-9d99-f4b8439aa372"
/><img width="58" height="338" alt="nord"
src="https://github.com/user-attachments/assets/053e8e7b-d639-4b72-92d2-ec7e2167aab8"
/><img width="58" height="338" alt="arc"
src="https://github.com/user-attachments/assets/3caeb07b-d41b-4d88-83b4-ef8d45d4e5a6"
/><img width="58" height="338" alt="solarized"
src="https://github.com/user-attachments/assets/6ebf6afb-ec3a-436b-90eb-bda40be1c79f"
/><img width="58" height="338" alt="light"
src="https://github.com/user-attachments/assets/fbb7f96a-b722-40c5-86fa-a0732e166972"
/><img width="58" height="338" alt="dark"
src="https://github.com/user-attachments/assets/5459208b-9256-4c55-9373-169e9cd9f09a"
/>

With labels
<img width="58" height="394" alt="labels"
src="https://github.com/user-attachments/assets/f97ee354-35cd-42b8-896f-57ac39644c1d"
/>

Logged out (only visible on desktop)
<img width="323" height="48" alt="logged out"
src="https://github.com/user-attachments/assets/75b71420-0c1b-446f-8cdd-43c68674d346"
/>

Logged in
<img width="355" height="48" alt="logged in"
src="https://github.com/user-attachments/assets/324fd133-a793-49dd-844a-f93dd5d1effb"
/>


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6381-UI-color-updates-tweaks-29b6d73d3650816384d2ef5617a776a0)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <[email protected]>
Co-authored-by: github-actions <[email protected]>

Author: 3 people