Convert GiftCardService to Typescript

Editor assessment

The type is wrong. Converting GiftCardService to TypeScript is behavior-neutral restructuring, so refactor(medusa) is the accurate classification; labeling it feat claims a new capability where none exists and will inflate the minor-version bump or insert a spurious 'Features' entry in generated changelogs. The subject itself is fine — imperative ('Convert'), concise, names the exact service, carries the PR reference — and the capitalized start is a trivial nit. 'Typescript' should be 'TypeScript', a detail that matters more in searchable logs than in prose. The repo demonstrably uses refactor for identical migrations elsewhere, so this is an inconsistency within its own history. No body, acceptable for a mechanical conversion; no breaking markers, correctly. Structurally valid, semantically mistyped — a textbook illustration of why type choice matters to automation.