fix: data CID is root CID of aggregate, not content CID

[alanshaw]

A regression from the DB migration.

See definition here:

web3.storage/packages/client/src/lib/interface.ts

Lines 202 to 205 in b865bfb

	/**
	* CID of the data aggregated in this deal.
	*/
	dataCid: string

...and old definition here:

web3.storage/packages/db/fauna/schema.graphql

Lines 306 to 313 in 2f9c86a

	"""
	An aggregate of content for inclusion in a Filecoin deal.
	"""
	type Aggregate {
	"""
	CID of the root of the aggregate data.
	"""
	dataCid: String! @unique