Add Kent release workflow infrastructure

[rovkinmax]

Summary

• add the unified Puber Release Kent Desktop workflow snapshot
• document release workflow policy and project contract outputs
• keep release workflow prompts compatible with origin/master worktrees by treating .kent/commands/release.md as supplementary until it exists in task base branches

Verification

• kent workflow validate --mode execution for all active Puber workflows
• jq empty for .kent/workflows/*.json
• git diff --check

Notes

This PR is needed because Kent task worktrees are created from origin/master. Without these .kent files on master, live Desktop workflows can reference files that task worktrees do not have.