Support row lineage assignment on commit

### Feature Request / Improvement

Part of #1551.

Set `first-row-id` and `added-rows` on new snapshots and enable V3 appends end-to-end. Validation and `next-row-id` advancement in `add_snapshot` are already merged.

Start at the add_snapshot entry point and trace the commit path for new snapshots and the V3 append flow. Ensure first-row-id and added-rows are assigned and V3 appends work end-to-end, while preserving the already-merged validation and next-row-id advancement.

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