[Refactor] Simplify parseGid using optional chaining and guard clause

[gonzaloriestra]

What does this PR do?

Refactors parseGid in packages/cli-kit/src/public/node/themes/utils.ts to replace explicit array index and undefined checks with optional chaining (GID_REGEXP.exec(gid)?.[1]) and an early error guard clause (if (!match)).

How to test your changes?

CI

Checklist

• I have evaluated the impact of this change and required tests.
• I have covered this change with unit tests.
• I have tested this change end-to-end.
• I have updated the documentation where applicable.

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PR created automatically by Jules for task 5538233410238856096 started by @gonzaloriestra

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