Replace prerelease onboarding authority with stable release metadata

[rmcdaniel]

Summary

• remove the retired qualified-onboarding workflow, manifest, and remote compatibility-document synchronizer
• use the checked-in stable source release record as the single version authority for Compose, Kubernetes, and Helm
• make the README quickstart use the public stable durableworkflow/server:2 channel
• retain drift checks so release tooling updates all generated consumers together

Validation

• 14 focused PHPUnit tests / 105 assertions pass
• 25 Helm release tests pass
• 3 Node 22 source-release tests pass
• source-release synchronization check passes
• public-boundary and diff checks pass
• durableworkflow/server:2 resolves from Docker Hub

Closes the failed obsolete onboarding path observed after #78 and advances durable-workflow/.github#115.