[Refactor] Simplify buildSessionChoices with early return and map

[gonzaloriestra]

What this PR does

Refactors buildSessionChoices in packages/cli-kit/src/public/node/session-prompt.ts to replace imperative loop mutation with an early return guard clause and a declarative .map() transform.

How to test your changes?

CI

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PR created automatically by Jules for task 2754549279388059089 started by @gonzaloriestra

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