Integrate Hopper for cross-chain market rebalancing UI

[starksama]

Summary

Add support for Hopper-based cross-chain market rebalancing in Monarch.

Scope (brief)

• Build a simple UI flow for cross-chain rebalancing.
• Let users review estimated fees before confirming.
• Wire to Hopper API/tooling for execution.

Reference API / docs

• https://gist.github.com/0xjuaan/ce6022c9f93616a7d41708672d2df359

Notes

Keep this implementation lightweight for v1; we can iterate later.