Prepare WordPress.org publishing

[priethor]

Part of #283.

Cortext should reach WordPress.org through the same release path we use for GitHub releases. Gutenberg is a good reference for the shape of this: build the ZIP first, publish the GitHub Release, then push to WordPress.org SVN behind a manual approval step. Cortext does not need Gutenberg's full RC/package machinery.

• Audit WordPress.org readiness: guidelines, plugin headers, readme.txt, license, stable tag, tested-up-to, and required metadata. Prepare Cortext copy and listing assets for the WordPress.org beta #314
• Prepare WordPress.org listing assets: icon, banner, screenshots, and screenshot captions. Prepare Cortext copy and listing assets for the WordPress.org beta #314
• Add an SVN publishing dry run for the approved plugin repository.
• Add a gated workflow for publishing a GitHub Release ZIP to WordPress.org SVN.
• Add a workflow or command for syncing WordPress.org assets to SVN /assets.
• Document the WordPress.org release runbook, including release confirmation after SVN tagging.
• Submit Cortext to WordPress.org and publish the first approved version. Preparation in Build: Tighten release packaging for WordPress.org #332 and Bug: descending order or relation fields doesn't work #335