fix: add network error retry for transfer polling

[jvsena42]

Fixes #608

This PR adds network error resilience to the transfer-to-spending polling mechanism by distinguishing between transient network failures and permanent order errors.

Description

• Uses .fold() instead of .getOrNull() to properly handle Result failures
• Implements a retry mechanism that tolerates up to 5 consecutive network errors before giving up
• Resets the error counter on successful fetches, allowing recovery from intermittent issues
• Preserves immediate exit behavior for permanent failures (order not found, order expired)

Preview

N/A - No UI changes

QA Notes

1. Normal transfer flow (regression)

1. Start a transfer to spending
2. Verify the setup steps progress (0 → 1 → 2 → 3)
3. Confirm the channel opens successfully

2. Network error recovery

1. Start a transfer to spending
2. Enable airplane mode briefly during polling
3. Disable airplane mode before 12.5 seconds (5 retries × 2.5s)
4. Verify polling resumes and completes successfully

3. Persistent network failure

1. Start a transfer to spending
2. Enable airplane mode and keep it enabled
3. After ~12.5 seconds, verify the transfer fails gracefully with appropriate logging