Fix[Settings]: Improve focus restoration after AI settings saves

[yogeshbhutkar]

What, Why, and How?

Similar to #532

This PR adds an interim focus-management fix for AI settings flows where the Save button disappears after saving. It restores keyboard focus to a related remaining control: the last inline settings field for inline feature settings, and “Reset to default” for developer model selection when that button is available. This avoids leaving keyboard and assistive technology users focused on an unmounted Save button.

This is not the ideal long-term UX. Disappearing action UI is inherently less predictable, and the settings page currently mixes save models: feature toggles and “Reset to default” save immediately, while developer settings and inline feature settings use explicit Save buttons. A better follow-up would be to unify settings changes through a shared store and provide one persistent Save action in the header, so all updates follow the same interaction model.

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5.5
Used for: Reviewing the code.

Testing Instructions

1. In the AI settings page, change an inline feature setting and click Save.
2. Confirm focus returns to the last field in that settings form.
3. Enable model selection, choose a provider/model, and click Save.
4. Confirm focus moves to “Reset to default” after Save disappears.

Screencast

screencast.mov

Changelog Entry

Fixed - focus restoration after AI settings saves.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.50%. Comparing base (4cbd972) to head (fde2a7f).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #812   +/-   ##
==========================================
  Coverage      75.50%   75.50%           
  Complexity      2086     2086           
==========================================
  Files             99       99           
  Lines           8626     8626           
==========================================
  Hits            6513     6513           
  Misses          2113     2113           

Flag	Coverage Δ
unit	75.50% <ø> (ø)

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[github-actions]

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Co-authored-by: yogeshbhutkar <yogeshbhutkar@git.wordpress.org>

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