Fix transaction history CoW API CORS errors

[alerodriargui]

General Changes

• Fixes transaction history failing to load when CoW order history requests are blocked by CORS
• Adds same-origin Next API proxy routes for CoW order history requests
• Keeps Aave transaction history available if CoW history fetching fails

Developer Notes

Fixes #2940.

The browser was calling https://api.cow.fi/.../account/.../orders directly, which could fail CORS preflight from https://app.aave.com. CoW history reads now go through app API routes instead.

Validation run:

• node_modules\.bin\tsc.cmd --noEmit --pretty false
• node_modules\.bin\eslint.cmd src\hooks\useTransactionHistory.tsx src\utils\cowOrderbook.ts pages\api\cow-orders.ts pages\api\cow-order.ts
• git diff --check

No new third-party packages or environment variables were added.

---

Reviewer Checklist

Please ensure you, as the reviewer(s), have gone through this checklist to ensure that the code changes are ready to ship safely and to help mitigate any downstream issues that may occur.

• End-to-end tests are passing without any errors
• Code changes do not significantly increase the application bundle size
• If there are new 3rd-party packages, they do not introduce potential security threats
• If there are new environment variables being added, they have been added to the .env.example file as well as the pertinant .github/actions/* files
• There are no CI changes, or they have been approved by the DevOps and Engineering team(s)

[vercel]

@alerodriargui is attempting to deploy a commit to the Aave Team on Vercel.

A member of the Team first needs to authorize it.