feat: #3616970 Release Varbase Components 4.0.0-rc1

Bump the README release badge to 4.0.0-rc1 ahead of tagging Varbase Components 4.0.0-rc1.

Supersedes the 4.0.0-beta5 badge merged in !64 (merged) — Varbase Components goes to 4.0.0-rc1 for the Varbase 11.0.0-rc1 train. The beta5 commit stays in history untagged; only 4.0.0-rc1 will be tagged.

Changes since 4.0.0-beta4:

• fix: #3615796 Resolve the PHPStan findings raised by the updated analyzers
• task: #3615770 Switch the Varbase functional testing suite to Varbase E2E
• task: #3615770 Update @vardot/varbase-e2e to the latest 2.x

Issue: #3616970

AI-Generated: Yes

Checkpoints:

• File an issue
• Addition/Change/Update/Fix
• Testing to ensure no regression
• Automated unit testing coverage
• Automated functional testing coverage
• UX/UI designer responsibilities
• Readability
• Accessibility
• Performance
• Security
• Developer Documentation
• User Guide Documentation
• Reviewed by human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release