Fix resume replay after history snapshots

[cbusillo]

Summary

• align resume replay against restored history snapshot suffix before rendering raw rollout items
• replay all raw items after the matched snapshot boundary, including user/tool records
• add regressions for stale assistant replay, user-tail snapshots, and repeated short assistant text

Validation

• cargo test --manifest-path code-rs/Cargo.toml -p code-tui replay_snapshot --features test-helpers
• ./build-fast.sh

Notes

The missing final answer was persisted in the rollout. The visible stale review came from snapshot replay re-appending older assistant messages before the restored transcript tail.