Finalize 2.0 release readiness

[DavidBabinec]

What changed

• make the release workflow build the WordPress application explicitly in production mode
• fail missing WordPress build configuration instead of exiting successfully without an artifact
• assert that the production Vite manifest exists before packaging
• publish the Core Framework 2.0.0 changelog in the WordPress.org readme, including the Oxygen 6.1 compatibility requirement
• align release documentation with the current single-maintainer deployment model
• refresh the Motion.page description in the project README

Why

The tag workflow previously relied on a local, ignored .env file. On a clean GitHub runner, the Vite configuration could create a development .env, exit successfully without building, and leave the release verification in an invalid state. WordPress.org also needed the 2.0.0 changes and Oxygen compatibility requirement in its parsed changelog.

Validation

• git diff --check
• clean missing-APP_ENV simulation exits non-zero
• APP_ENV=production bun run build:wp
• production manifest assertion
• bun run check:open-source
• rebuilt core-framework-2.0.0.zip
• 147 web tests passed
• 21 PHP tests passed
• fresh WordPress 7.0.4 / PHP 8.2 install passed
• official WordPress.org 1.10.4 to 2.0.0 single-site and multisite upgrade matrix passed