Add engine bakeoff ownership plan

[RollNuts]

Summary

• Add ownership guidance for engine bakeoff execution.
• Split Unity fresh slice and Unreal 5.8 fresh slice into separate PRs/owners.
• Reuse prohibition for existing Unity mock and existing Unreal hotel project.
• Define required evidence: gameplay screenshot, close attack screenshot, 10s capture, asset ledger per engine.
• Add engine decision gate and request Veripsa Core for PR merge order review.

Relates #6
Relates #7
Relates #8

Request

Please review PR merge order for Veripsa Core before merge.

[RollNuts]

Veripsa Core request: please include this PR in merge-order planning with #10, #11, #13, and #14. This PR defines Unity/Unreal bakeoff ownership and relates #6/#7/#8. Please flag whether this should merge before implementation PRs and whether Unity/Unreal need separate agent branches.