[Refactor] Improve session scope generation logic

[gonzaloriestra]

Refactored the session scope generation logic in packages/cli-kit/src/private/node/session/scopes.ts to use modern array methods and project utilities. Specifically, replaced map().flat() with flatMap() and manual unique array generation with the uniq() helper.

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PR created automatically by Jules for task 15483759258803923353 started by @gonzaloriestra

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