AI settings: report SEO enhancer availability

[ariskataoka]

Addresses backend for #50386 (comment)

Proposed changes

• The feature-settings endpoint reports seo_enhancer.available, so the settings page can hide the AI SEO row where the enhancer can't run.
• The gate mirrors the legacy Traffic page: the ai_seo_enhancer_enabled filter, the seo-tools module (Modules::is_active() — always true on Simple), and the ai-seo-enhancer plan feature. Happy to drop the module term if you'd rather match the newer packages/seo formula (filter + plan only).

Does this pull request change what data or activity we track or use?

No

Testing instructions

• GET wpcom/v2/jetpack-ai/feature-settings as admin → features.seo_enhancer.available is true on a plan with the feature and the seo-tools module active.
• Deactivate the SEO Tools module (or test on a plan without ai-seo-enhancer) → available flips to false

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the add/jetpack-ai-seo-enhancer-availability branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/jetpack-ai-seo-enhancer-availability

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

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[jp-launch-control]

Code Coverage Summary

No summary data is available for parent commit 40b87e8, so cannot calculate coverage changes. 😴

If that commit is a feature branch rather than a trunk commit, this is expected. Otherwise, this should be updated once coverage for 40b87e8 is available.

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