Upgrade dry-run + storage-layout compatibility check in CI

[joelpeace48-cell]

Epic: Contract Safety & Hardening

Summary

Simulate an upgrade in CI and assert storage layout stays compatible or a migration exists.

Background & Problem

Unsafe upgrades can brick state; automated checks catch incompatibilities pre-deploy.

Acceptance Criteria

• CI simulates upgrade + checks layout.
• Incompatibility without migration fails.

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Filed as part of the mainnet-readiness & world-class roadmap. Scope is intentionally small enough for one focused PR; comment to claim.