Add MCP settings to site settings endpoint

[eoigal]

Add MCP (Model Context Protocol) settings to the site settings endpoint.

Proposed changes:

• Added mcp_abilities field to site settings API (GET/POST support)
• Includes MCP enabled toggle and per-ability configuration
• Added test coverage for new functionality

Structure:

{
  "mcp_abilities": {
    "ability-name": {
      "name": "...",
      "description": "...", 
      "category":"...",
      "type":"...",
      "enabled": true/false
    }
  }
}

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

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

Testing instructions:

• Tests included
• Go to https://developer.wordpress.com/docs/api/console/
• Apply JP PR to WPCOM sandbox with bin/jetpack-downloader test jetpack add/mcp-settings
• Sandbox public-api.wordpress.com
• Enter GET /sites/$site/settings for a test site, confirm you see settings below

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add a "[Type]" label (Bug, Enhancement, Janitorial, Task).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

---

Follow this PR Review Process:

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[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/mcp-settings branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/mcp-settings

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

[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/json-endpoints/class.wpcom-json-api-site-settings-endpoint.php	388/845 (45.92%)	2.88%	11 💔
projects/plugins/jetpack/json-endpoints/class.wpcom-json-api-site-settings-v1-4-endpoint.php	0/167 (0.00%)	0.00%	1 ❤️‍🩹
projects/plugins/jetpack/class.json-api.php	43/474 (9.07%)	1.69%	-8 💚

Full summary · PHP report · JS report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}

[tbradsha]

@eoigal Note that I added wp_get_abilities() stubs from WP.com in #44976, so no need to suppress them in Phan anymore.

[eoigal]

Will add stubs for new AbilityRegistry functions in a follow up p1756730969998889-slack-CDLH4C1UZ

191683-ghe-Automattic/wpcom