Shared adapter execution for sync and Oban worker dispatch paths.

Phase 14 contract changes (D-05)

classify/1 now returns a 3-tuple {outcome, error_class, detail} so :temporary | :permanent | :bounced classification is preserved end-to-end:

adapter.deliver -> classify -> Deliveries.record_attempt(error_class:)
                            -> attempt row .error_class column
                            -> trace explanation
                            -> Oban worker {:ok | {:error, _}} return

run_delivery/1 passes error_class into Deliveries.record_attempt/2. The return shape is unchanged for sync consumers ({:ok, %{delivery, attempt}} | {:error, step, reason, changes} | {:error, term()}). Plan 14-05's Oban worker reads the recorded attempt's outcome + error_class to decide its Oban return value (retry vs terminal vs success).