docs: finalize v2 release readiness

[bxvtr]

Summary

• mark Version 2 as the current architecture and canonical deployment path
• record successful end-to-end live clean-room acceptance
• preserve historical V1 and defect chronology
• retain still-true architectural and external-foundation limitations

Live acceptance evidence

• fresh Cloud Shell and fresh clone
• Greenfield deploy
• resumability after PR fix: avoid unnecessary system pip dependency #75
• second convergence changed=0
• reboot proof and post-reboot recovery
• reviewed destroy
• empty Terraform state
• fresh create/add-only plan
• external state bucket preserved with Versioning Enabled and NoPublicAccess
• external Vault preserved ACTIVE
• post-destroy create plan not applied

Scope

• documentation/status only
• no Terraform/Ansible/Argo/Kubernetes implementation changes
• no tools/workflows/tests changes
• no tag or release created
• [Unreleased] preserved

Review

• independent PRE-COMMIT review approved
• BLOCKER=0 HIGH=0 MEDIUM=0 LOW=1 INFO=2
• LOW is wording-only and intentionally not changed after review