…dpoint (#28088)

## **Description**

<!-- 1. What is the reason for the change? The fallback URL for
`DIGEST_API_URL` was pointing at the development endpoint. -->
<!-- 2. What is the improvement/solution? Switch the hardcoded fallback
to the production endpoint so that builds without an explicit env var
hit production. -->

Switches the hardcoded fallback value for `DIGEST_API_URL` in
`AppConstants.ts` from the dev endpoint
(`digest.dev-api.cx.metamask.io`) to the production endpoint
(`digest.api.cx.metamask.io`).

Also moves the `@metamask/sdk-communication-layer` import to the top of
the file to follow alphabetical import ordering.

## **Changelog**

CHANGELOG entry: null

## **Related issues**

Fixes:

## **Manual testing steps**

N/A

## **Screenshots/Recordings**

### **Before**

N/A

### **After**

N/A

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- Generated with the help of the pr-description AI skill -->

Made with [Cursor](https://cursor.com)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: only changes a constant fallback URL and import ordering.
Main impact is that builds without `DIGEST_API_URL` will now call the
production digest service instead of the dev endpoint.
> 
> **Overview**
> Updates `AppConstants.DIGEST_API_URL` to default to the production
`https://digest.api.cx.metamask.io/api/v1` endpoint when the
`DIGEST_API_URL` env var is not set.
> 
> Also reorders the `DEFAULT_SERVER_URL` import to match expected import
ordering.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
9d584a4. This will update automatically
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[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->