Improve resilience of transaction submission by handling transient broadcast failures

## Problem

Transaction submission currently fails immediately if broadcasting to the orderer returns an error.

In distributed environments, transient failures such as:
- temporary network interruptions
- brief unavailability of the orderer
- short-lived timeouts

can cause a transaction submission to fail even though a retry would likely succeed.

## Proposed Solution

Introduce a minimal retry mechanism for transaction broadcast in:

- SubmitTransaction
- SubmitTransactionWithWait

Key considerations:
- Retry a small fixed number of times (e.g., 2–3 attempts)
- Add a short delay between attempts
- Respect context cancellation (stop retrying if context is done)
- Preserve existing behavior if all retries fail

## Why this matters

- Improves reliability of transaction submission
- Reduces failures caused by transient conditions
- Aligns with common practices in distributed systems

## Scope

- Limited to tools/fxconfig/internal/app/submit.go
- No changes to public APIs
- Initial implementation can use fixed retry parameters

## Additional Context

This builds on the current submission flow and focuses on improving robustness without introducing breaking changes.