Deploy stable releases to WordPress.org after publish

[priethor]

What

Related to #365.

Publishing a stable GitHub Release now kicks off the WordPress.org deploy. It still stops at the right places: first the SVN dry run, then the `wordpress-org` approval before anything is committed. Prereleases stay out of wp.org.

Why

This makes the release flow less manual without removing the two checks that matter: read the draft before publishing it, then review the SVN diff before approving the deploy.

How

• Pin draft Releases to the prepared release ref when the orchestrator passes one.
• Let the existing wp.org deploy workflow run from stable release events as well as manual dispatch.
• Check the version, prerelease state, and `cortext.zip` before touching SVN.

Testing Instructions

1. From the Actions tab, run "Deploy to WordPress.org SVN" for an existing stable version with `commit=false`.
2. Confirm the dry run completes and the publish job is skipped.
3. On the next stable release, publish the draft Release and confirm the deploy workflow starts, runs the dry run, and waits for `wordpress-org` approval before committing to SVN.