v0.8.0

Adds a transaction-scoped client: Client.InTxn(tx) and typed.Client[T].InTxn(tx) return clients whose full surface runs inside a caller-managed transaction (reads join the read-set; writes stage; commit via tx.Commit()), plus typed.Client[T].NewTxnContext. A typed WhereEdge query built via InTxn runs its edge pre-pass in the same transaction. BREAKING: v0.7.0's TxnContext.Insert/Upsert/Update are removed — those Client-level writes now live on the scoped InTxn client; TxnContext keeps lifecycle + graph primitives (DeleteEdge/DeleteNode/DeletePredicate). See CHANGELOG.