Exercise export/import, snapshot restore, and mainnet-state rehearsal for v31

[juno-ai-dev]

Scope

Define supported voting-snapshot/FeePay export invariants, test restart/snapshot/state-sync/export-import after upgrade, and create a sanitized reproducible mainnet-state rehearsal record.

Acceptance criteria

• FeePay state round-trips and remains module-account backed.
• Voting power rebuild/history behavior is tested and documented.
• Exact v30.0.0→v31 upgrade, restart, restore, state sync, and export/import pass invariants.
• Evidence records commits, image digests, snapshot height/hash, version maps, app hashes, durations, and probes.
• No credentials are stored.

Dependency: stable dependency graph and v31 handler.