Phase 7.17: prepare 2.0.0-alpha.1 release

[josiahking]

Summary

Prepare the EvolvePHP 2.0.0-alpha.1 release documentation and acceptance contract.

This change:

• adds the dated 2.0.0-alpha.1 section to the changelog while keeping Unreleased empty for future work
• marks the Alpha release notes with the exact version, stage, release date, and tag identity
• preserves the PHP 8.4 minimum and PHP 8.4/8.5 compatibility statement
• keeps the Alpha explicitly experimental and not recommended for production
• keeps first-party packages documented as not independently published
• updates the README release-notes link from draft wording
• updates the existing documentation contract test for the released-state documentation

Boundaries

This change does not:

• modify framework runtime or package source
• change Composer manifests, package topology, or release-package mapping
• publish first-party packages
• create or push the 2.0.0-alpha.1 tag
• publish a GitHub release
• claim public Packagist availability
• claim production readiness

The tag and GitHub pre-release remain separate release actions after the accepted merge commit is verified.

Validation

Validated on PHP 8.4 with:

• strict root Composer and lock validation
• strict legacy-client Composer validation
• focused Alpha documentation contract: 10 tests, 240 assertions
• twelve-package release inventory validation
• deterministic package-split validation for all 12 packages
• prerelease-consumer validation
• application skeleton create-project validation
• supply-chain validation
• root quality: 963 tests, 3,997 assertions, 1 skipped; PHPStan, Deptrac and PHP-CS-Fixer clean
• committed diff and release-metadata integrity checks

The dedicated pull-request CI remains responsible for the real PHP 7.4 legacy-client runtime proof.