Add assistant thinking state and logic.

[chase-west]

Fixes #4

Currently this uses a timer to reset the thinking variable. Would be best practice to dynamically update it as well as the duration for the thinking toast; probably wouldn't be too hard to implement.

[vercel[bot]]

Someone is attempting to deploy a commit to a Personal Account owned by @ntegrals on Vercel.

@ntegrals first needs to authorize it.

[ntegrals]

@chase-west Thanks for the PR. Super helpful 🙌