feat: Chat API and design refinements

[devongovett]

WIP in case someone wants to pick this up.

• Adjusts spacing to match design specs
• Adds scroll fade on the thread
• Moves some styles from the stories into the Chat/Thread components and generally simplifies the API

TODO:

• look at inline TODO comments in code, mostly API questions
• decide if we want to have a "style-less" version as well
• update docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the S2 docs
• View the React Aria docs

[rspbot]

Agent Skills Changes

Modified (9)

• react-aria/agent-skills/index.json $\color{green}{+1}$ $\color{red}{-1}$
• react-aria/agent-skills/react-aria.tar.gz
• react-aria/agent-skills/react-aria/references/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/index.json $\color{green}{+3}$ $\color{red}{-3}$
• s2/agent-skills/migrate-react-spectrum-v3-to-s2.tar.gz
• s2/agent-skills/react-spectrum-s2.tar.gz
• s2/agent-skills/react-spectrum-s2/references/guides/ai-components.md $\color{red}{-17}$
• s2/agent-skills/react-spectrum-s2/references/react-aria/components/Separator/useSeparator.md $\color{green}{+1}$ $\color{red}{-1}$
• s2/agent-skills/spectrum-audit.tar.gz

Install

React Spectrum S2:

npx skills add https://d1pzu54gtk2aed.cloudfront.net/pr/ac3c85640f53d798bd2b9974784cee3b2c9d9add/

React Aria:

npx skills add https://d5iwopk28bdhl.cloudfront.net/pr/ac3c85640f53d798bd2b9974784cee3b2c9d9add/