Add WordPress Playground demo blueprint

[s3rgiosan]

Description of the Change

Adds a WordPress Playground blueprint (.github/blueprints/blueprint.json) that spins up a live, zero-install demo of WP Content Connect directly in the browser. Opening the blueprint boots a fresh WordPress instance, installs and activates the plugin, seeds example content, and drops the user straight into wp-admin — letting reviewers, contributors, and users try post-to-post and post-to-user relationships without a local environment.

The blueprint:

• Targets PHP 8.3 and the latest WordPress release.
• Enables networking (required to pull the plugin ZIP and example-data repo) and auto-login.
• Installs WP Content Connect from the develop branch ZIP and activates it into wp-content-connect.
• Installs the companion wp-content-connect-example-data plugin from Git (main) to provide the WP-CLI seeder.
• Runs wp content-connect-example generate --universities=10 --cities=20 --people=100 to populate demo posts and users with real relationships.
• Lands on /wp-admin/.

Benefits: instant, reproducible demo environment; lower barrier for evaluating the plugin; a shareable link for issues/support.

Closes #

How to test the Change

1. Open the blueprint in Playground, e.g. https://playground.wordpress.net/?blueprint-url=<raw-url-to-.github/blueprints/blueprint.json> (or via the "Preview in Playground" flow once merged).
2. Confirm WordPress boots to /wp-admin/ already logged in, on PHP 8.3 + latest WP.
3. Confirm WP Content Connect and the example-data plugin both show as active under Plugins.
4. Confirm seeded content exists (universities/cities/people posts and users) and that relationship panels render on those posts.
5. Verify the blueprint validates against the schema ($schema resolves, no console errors in the Playground boot log).

Changelog Entry

Developer - Add a WordPress Playground blueprint for a one-click, zero-install plugin demo.

Credits

Props @s3rgiosan

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.