Add typed JSON output to hydrogen deploy

[gonzaloriestra]

WHY are these changes introduced?

Deployment needs a finite result that reports successful and declined operations consistently.

Fixes https://github.com/shop/issues-develop/issues/23679

WHAT is this pull request doing?

Return {status, deployment} with validated URLs and null unavailable bypass tokens. Preserve the native Oxygen CompletedDeployment bytes in h2_deploy_log.json; --json-output still controls that CI file independently from --json.

HOW to test your changes?

shopify hydrogen deploy --json-schema
shopify hydrogen deploy --json

Checklist

• I have read the contributing guidelines
• I have considered cross-platform impacts
• I have added a changeset for user-facing changes
• I have added tests
• I have updated the documentation

[shopify]

Oxygen deployed a preview of your gonzalo/hydrogen-json-deploy branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	October 13, 202611:04 AM

Learn more about Hydrogen's GitHub integration.

[fredericoo]

nice and simple - splitting executeDeploy from the presenter in runDeploy reads well, human-mode output is unchanged, and h2_deploy_log.json keeps the same bytes and stays independent of --json (with a test for it). Errors go through the shared JSON error path from #4095, and the two helpers that used to warn-and-return now throw in JSON mode so we don't end up emitting null for what's really a failure.

a couple of small comments on the JSON-mode custom build hook, otherwise LGTM