Add game seeding scripts for multiproof testing

[leopoldjoy]

Summary

• Adds SeedGames.s.sol Foundry script that pre-populates the DisputeGameFactory with chained AggregateVerifier games using real L2 output roots
• Adds generate-roots.sh bash script that fetches real output roots from an L2 archive node via optimism_outputAtBlock
• Updates scripts/multiproof/README.md with a 5-step guide for the full seeding workflow

These scripts are useful for testing forward traversal at proposer restart — the proposer can walk the linked list of games to find where to resume. Games use ProofType.ZK with the MockVerifier (which auto-accepts), while the output roots are real values from the L2 chain.

[cb-heimdall]

✅ Heimdall Review Status

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