Respect wp_supports_ai() and improve AI-disabled notice in Namer

[raftaar1191]

What?

Closes #1222

This PR updates the Plugin Check Namer flow to respect WordPress AI support controls and present clearer UI messaging when AI functionality is unavailable.

Why?

The Namer tool should not initialize AI-dependent behavior when AI is disabled at the site level (for example via WP_AI_SUPPORT or the wp_supports_ai filter). This aligns Plugin Check with core AI capability controls and avoids confusing behavior for site administrators.

How?

• Refactors AI readiness checks in AI_Utils into dedicated methods:
  • check_ai_prerequisites()
  • check_ai_connectors()
  • get_ai_config() as orchestrator
• Adds an explicit wp_supports_ai() prerequisite check (when available) and returns a specific WP_Error when AI is disabled.
• Keeps connector checks separate so UI can decide whether to show the “Configure AI Connectors” CTA only when prerequisites are met but connectors are missing.
• Updates Namer page rendering to show the concrete prerequisite/connector error message and conditionally show connector setup action.

Use of AI Tools

I used GitHub Copilot (GPT-5.3-Codex) to assist with drafting/refactoring code and preparing the PR text. I reviewed and validated the final changes manually.

Testing Instructions

1. Install and activate Plugin Check on a WordPress 7.0+ site.
2. Visit Tools → Plugin Check Namer.
3. Confirm normal behavior with AI support enabled and a connector configured.
4. Disable AI support (for example by filtering wp_supports_ai to false).
5. Reload the Namer page and verify an error notice appears indicating AI support is disabled.
6. Re-enable AI support but remove/disable AI connectors.
7. Reload the Namer page and verify connector-related guidance appears with a Configure AI Connectors button.
8. Run PHPCS on the changed files and confirm no new violations.

Testing Instructions for Keyboard

1. Navigate to Tools → Plugin Check Namer using keyboard only.
2. Verify focus order reaches the notice and action button when shown.
3. Activate the Configure AI Connectors button using keyboard (Enter/Space) and confirm navigation works.

Screenshots or screencast

PR.proof.for.1222.mp4

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

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