Documentation: Contract deployment and rollback playbook

[Cedarich]

Complexity: 150 points

Goal
Write a deployment and rollback playbook for the Soroban contract suite so maintainers can manage testnet changes consistently.

Acceptance Criteria

• Documents deploy prerequisites and contract ordering.
• Includes rollback or emergency-halt guidance.
• References canonical contract manifest handling.
• Clear enough for contributors to follow without tribal knowledge.