settings_ui: Fix layout issues with recently created GitHub accounts (#63630)

# Objective

Fixes #62169

Accounts which are marked "too young" have layout issues within the LLM
settings. Example provided in the linked issue.

## Solution

Allow the provider controls to shrink to the available width instead of
retaining their content width. Also make the young-account configuration
fill that width so the warning wraps correctly without collapsing the
provider description.

I think the "Upgrade to Pro" looks a little stretched now, but I don't
know how to fix it without allocating even more space for the already
large setting section. Could we possibly shorten the 30-day requirement
explanation? Regardless, it's much better than what it was before :D

## Testing

- I added a debug selector to be able to write a regression test for
layout issues. Since the UI may change, the tests only enforce the rough
layout.
- Compiled with `too_young_account` being `true` and `false`, checking
that the UI looks okay.


## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase

<details>
  <summary>Click to view showcase</summary>

Before:

<img width="639" height="678" alt="image"
src="https://github.com/user-attachments/assets/45ed32b0-8987-49d1-8bbd-a12f7917570a"
/>


After:

<img width="640" height="225" alt="image"
src="https://github.com/user-attachments/assets/bb39a847-7d36-4597-b16d-6a6ccb872817"
/>

</details>

---

Release Notes:

- Fixed layout issues in settings when using recently created GitHub
accounts

---------

Co-authored-by: MrSubidubi <finn@zed.dev>
59b0c714fftidely committed on 9/3/2026, 3:16:07 PM· committed by GitHubparent5b055fa
5 files changedLine totals unavailable