[Refactor] Use async/await and early returns in errorHandler

[gonzaloriestra]

WHY are these changes introduced?

This is a cleanup refactor to improve the readability and maintainability of the errorHandler function in cli-kit.

WHAT is this pull request doing?

Refactors errorHandler in packages/cli-kit/src/public/node/error-handler.ts:

• Replaces a nested if/else if/else structure with early return guard clauses.
• Converts a .then() promise chain into async/await syntax.
• Removes redundant variable shadowing in the promise chain.

How to test your changes?

CI

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 15958592844892288088 started by @gonzaloriestra

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