feat(devex): add Cursor worktree setup configuration (MetaMask#26986)

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## **Description**

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Write a short description of the changes included in this pull request,
also include relevant motivation and context. Have in mind the following
questions:
1. What is the reason for the change?
2. What is the improvement/solution?
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1. **Reason**: When using Cursor's worktree feature to run agents in
separate checkouts, each worktree needs the same env files and plan
files as the main repo so that install/build and agent context work
correctly.
2. **Solution**:
  - Add `.cursor/worktrees.json` so that when Cursor creates a worktree
- Add setup commands that copy `.js.env`, `.ios.env`, `.android.env`,
`.e2e.env`, and `.cursor/plans` (recursively as it's a folder) from the
root repos into the new worktree.

## **Changelog**

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`CHANGELOG entry: Fixed a bug that was causing some NFTs to flicker`

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CHANGELOG entry: null

## **Related issues**

Fixes: N/A

## **Manual testing steps**

```gherkin
Feature: Cursor worktree setup

  Scenario: worktree is created with env and plans copied
    Given the repo has .cursor/worktrees.json configured

    When dev creates a new agent tab using "worktree" agent location
    And Cursor creates a new worktree
    Then .js.env, .ios.env, .android.env, .e2e.env and .cursor/plans (and content) exist in the worktree
```

## **Screenshots/Recordings**

The worktree menu available when creating a new local chat agent:
<img width="266" height="274" alt="image"
src="https://github.com/user-attachments/assets/67e7c406-b6f4-4220-aaf3-4f00ec1ba98b"
/>

## **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.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk developer-experience change that only adds a Cursor
configuration file and does not affect runtime app behavior. Main risk
is overwriting local env/plan files in worktrees if users have
customized them.
> 
> **Overview**
> Adds `.cursor/worktrees.json` to configure Cursor’s *worktree* setup
so new worktrees automatically copy `.js.env`, `.ios.env`,
`.android.env`, `.e2e.env`, and `.cursor/plans` from the root worktree
into the new checkout.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
85347a6. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: NicolasMassart

.cursor/worktrees.json

@@ -0,0 +1,9 @@
+{
+  "setup-worktree": [
+    "cp $ROOT_WORKTREE_PATH/.js.env .js.env",
+    "cp $ROOT_WORKTREE_PATH/.ios.env .ios.env",
+    "cp $ROOT_WORKTREE_PATH/.android.env .android.env",
+    "cp $ROOT_WORKTREE_PATH/.e2e.env .e2e.env",
+    "cp -r $ROOT_WORKTREE_PATH/.cursor/plans .cursor/plans"
+  ]
+}