Add save button to developer settings panel (Provider/Model selectors)

[Infinite-Null]

What?

Closes #763

Adds an explicit Save button to the Developer Settings panel (Provider/Model selectors), instead of saving changes immediately on every selection.

Why

Provider and Model changes were being saved as soon as you picked a new option, with no confirmation step. This was inconsistent with the rest of the settings UI, where changes are only saved when you click Save. A moderator flagged this during review.

How to test

1. Navigate to AI Settings and enable Enable AI.
2. Open the Developer Tools menu (three dots) and select Model selection.
3. Change the Provider or Model.
4. Confirm a Save button appears and the change is not saved yet.
5. Click Save and confirm the change persists.
6. Confirm clicking on "Reset to default" shows a Save button, and Save still behaves as expected.

Before / After

Before: Selecting a new Provider or Model saved it instantly.
After: Selecting a new Provider or Model shows a Save button; the change is only saved when you click it.

Screenshots / Recording

Before

Screen.Recording.2026-06-23.at.5.26.45.PM.mov

After

Screen.Recording.2026-06-23.at.5.21.27.PM.mov

Changelog Entry

Added - New feature.
Changed - Existing functionality.
Deprecated - Soon-to-be removed feature.
Removed - Feature.
Fixed - Bug fix.
Security - Vulnerability.
Developer - Development related updates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.41%. Comparing base (27e202b) to head (8e33f57).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #761   +/-   ##
==========================================
  Coverage      76.41%   76.41%           
  Complexity      1828     1828           
==========================================
  Files             87       87           
  Lines           7764     7764           
==========================================
  Hits            5933     5933           
  Misses          1831     1831           

Flag	Coverage Δ
unit	76.41% <ø> (ø)

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[github-actions]

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[dkotter]

Couple minor things but overall this looks good.

Ideally we get some E2E tests here though, to verify the new save button works and to also verify if you choose a provider/model and don't hit save, those values don't persist on page reload

[dkotter]

Looks like we're inconsistent with the fallback here, some places use 16px some use 12px. Should standardize that