Explain iETH and where protocol swaps execute

Consolidates feedback tickets #145 (https://app.notion.com/3b199411cf9081d7ad0cce3f6869b5bd) and #147 (https://app.notion.com/3b199411cf90819faa3cec7aa6896352). Reported after successful swaps on Chrome and iOS.

## Problem

Users can complete a MIDEN → iETH swap but are left asking:

- What is iETH?
- How does it relate to ETH?
- Where did the exchange execute?
- What does “protocol DEX” mean in practical terms?

## Expected

Before confirmation and in the result/detail view, explain the output asset and execution venue in concise user-facing language. The explanation should be sufficient for someone who is not already familiar with Miden’s asset naming or native DEX.

Feedback DB refs: tickets 145 and 147.