[Portal] Fix Transactions link in Archived Documentation section (#8574)

https://linear.app/thirdweb/issue/PRO-149/fix-archive-link-for-transactions

Update the Transactions link to point to /engine instead of /wallets/server/send-transactions.

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## PR-Codex overview
This PR focuses on updating the `href` property of the `ArticleCardIndex` component in the `page.tsx` file to redirect users to a new location.

### Detailed summary
- Changed the `href` property of the `ArticleCardIndex` from `"/wallets/server/send-transactions"` to `"/engine"`

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<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

* **Chores**
  * Updated the Transactions card navigation link destination in the Archive section.

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Author: eabdelmoneim

apps/portal/src/app/page.tsx

@@ -96,7 +96,7 @@ function ArchiveSection() {
         />
         <ArticleCardIndex
           description="Transactions knowledge base and guides"
-          href="/wallets/server/send-transactions"
+          href="/engine"
           icon={ArchiveIcon}
           title="Transactions"
           external