UX: Update AI Connector notice to warning style

[prasadkarmalkar]

What?

Closes #564

This PR updates the AI Connector notice on the settings page from a destructive/red error styling to a yellow warning styling.

Why?

Currently, the notice indicating that no AI Connectors are configured is displayed using a red error banner.

How?

• Changed the intent prop on <Notice.Root> from "error" to "warning" in stage.tsx

Use of AI Tools

Testing Instructions

1. Clear or deactivate all configured AI Connectors in your WordPress administration dashboard.
2. Navigate to the AI plugin settings page.
3. Verify that the notice at the top is displayed with a warning/yellow styling and a caution icon instead of a destructive/red alert.

Screenshots or screencast

Before	After

Changelog Entry

Changed - Update AI Connector setup notice styling from error to warning.

[github-actions]

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Co-authored-by: prasadkarmalkar <prasadkarmalkar@git.wordpress.org>
Co-authored-by: raftaar1191 <raftaar1191@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.21%. Comparing base (19ae2eb) to head (49c931f).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #565   +/-   ##
==========================================
  Coverage      71.21%   71.21%           
  Complexity      1151     1151           
==========================================
  Files             67       67           
  Lines           5565     5565           
==========================================
  Hits            3963     3963           
  Misses          1602     1602           

Flag	Coverage Δ
unit	71.21% <ø> (ø)

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