docs: add data workflow guidance

[adnqcr7-code]

What

Adds guidance for importing datasets while offline, including content hashes, schema versions, idempotent retries, and explicit conflict states.

Verification

Documentation-only change. No runtime behavior changed.

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[github-actions]

No activity on this PR for 14 days. In this repo PRs normally merge within the hour, so a quiet branch is usually one whose work has already landed another way.

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