feat(vercel-sandbox): support new Snapshot.fromSandbox method

[marc-vercel]

Support the new static method Snapshot.fromSandbox(...) to get the latest snapshot of a sandbox. Example:

const childSandbox = Sandbox.create({
  source: {
    type: 'snapshot',
    snapshotId: Snapshot.fromSandbox('main-sandbox')
  }
});

At the CLI level, is it with the parameter --sandbox-snapshot. It follows the same pattern as --snapshot. I do not think this is 100% clear and maybe we should iterate to sandbox create --from-snapshot and sandbox create --from-sandbox-snapshot?

For example:

> sandbox create --sandbox-snapshot main-sandbox

[vercel]

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Project	Deployment	Actions	Updated (UTC)
sandbox	Ready	Preview, Comment, Open in v0	Apr 27, 2026 4:15pm
sandbox-cli	Ready	Preview, Comment, Open in v0	Apr 27, 2026 4:15pm
sandbox-sdk	Ready	Preview, Comment, Open in v0	Apr 27, 2026 4:15pm
sandbox-sdk-ai-example	Ready	Preview, Comment, Open in v0	Apr 27, 2026 4:15pm
workflow-code-runner	Ready	Preview, Comment, Open in v0	Apr 27, 2026 4:15pm