fix: Fix useTx AbortSignal propagation to actual fetch cancellation

[joseph0926]

Problem

In packages/tx/src/hooks.ts:

abortControllerRef is created but signal is not passed to Transaction
Network requests (fetch) are not actually cancelled when transaction is aborted

Proposed Solution

Pass signal to Transaction.run() via request(variables, { signal })
Either connect external signal to Transaction or provide tx.cancel() method
Clarify in docs and implementation: "Does failed step's compensate execute?" (currently only successful steps are rolled back)

Affected Files

packages/tx/src/hooks.ts
packages/tx/src/transaction.ts