Add ordinals to paginated rollout records

[copyberry]

Add ordinals to paginated rollout records

Why

Paginated thread history needs durable ordering so consumers can process a rollout suffix without rebuilding all earlier history.

What changed

• Add optional, zero-based ordinals to RolloutLine records in paginated rollouts while leaving legacy rollout serialization unchanged.
• Continue ordinals from the last valid record when appending or resuming, including after gaps or an incomplete tail, and reject overflow without appending.
• Add a stateless project_rollout_line helper that maps canonical turn lifecycle and completed-item records into thread-history change sets.

Testing

• Cover ordinal assignment, legacy compatibility, resume and tail recovery, overflow handling, and thread-history projection for completed, failed, and interrupted turns.