[Refactor] Use uniq helper in app management client

[gonzaloriestra]

WHY are these changes introduced?

This refactor replaces manual Array.from(new Set(...)) deduplication logic with the standardized uniq helper from @shopify/cli-kit/common/array. This improves code consistency and readability by using existing project utilities.

WHAT is this pull request doing?

• Imports the uniq helper in packages/app/src/cli/utilities/developer-platform-client/app-management-client.ts.
• Replaces manual Set-based deduplication for allBetaFlags and allExpFlags in the allowedTemplates function with the uniq utility.

How to test your changes?

CI

Post-release steps

None.

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 11757100007447729076 started by @gonzaloriestra

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