iOS: auto-consume of MIDEN notes stops when Delegate Proof Generation is disabled

## Symptom

On iOS, disabling **Delegate Proof Generation** stops MIDEN notes from being auto-consumed, even though **Auto Consume MIDEN notes** is still enabled. No error is shown; notes just stay pending.

## Steps to reproduce

1. iOS app, Auto Consume MIDEN notes enabled (default).
2. Disable Delegate Proof Generation in General Settings.
3. Receive a MIDEN note.
4. Note is not auto-consumed.

## Expected

Auto-consume should work regardless of the proving mode — with delegation off it should consume via the native local prover.

## Notes

Auto-consume is not intentionally gated on the delegation setting (`Explore.tsx` passes the flag through to `initiateConsumeTransaction`). Suspect the local-proving consume fails on iOS and the auto-consume bounded-retry backoff gate in `initiateConsumeNotesTransaction` (`src/lib/miden/transaction/initiate.ts`, from #215) then silently suppresses further attempts. Not yet reproduced live.

Feedback DB ref: ticket 118. Possibly related: tickets 77 (Android notes unclaimable after failed local-proving consume) and 92 (iOS "nothing to claim" notification).