Show current liquidation price in edit margin modal

[JeremyZeng77]

Fixes #4

Summary

• add the current liquidation price to the Edit Margin modal
• keep the existing projected/new liquidation price row below it so users can compare before submitting an add/remove margin action

Verification

• git diff --check
• npm run build

Bounty payout

USDT TRC20: TWupTAoFjxR2VmqUUvzhfmUwXVZR6Kvz1Y
PayPal fallback: https://paypal.me/Jeremytsangchina

[JeremyZeng77]

Local verification passed with git diff --check and npm run build.

The only failing GitHub status I see is Vercel with Account is blocked., which appears to be an external project/account deployment issue rather than a code failure in this branch.