feat: support for commercial imagen3 node

[psychedelicious]

Summary

• Extend model taxonomy for API models.
• Allow nodes to be clobbered with a warning.
• Port bbox aspect ratio component to a native select (probably didn't need to do this but it made sense in the moment)
• Add graph builder for imagen3 commercial node. Some type checking is disabled bc the node isn't available in OSS, so there are no autogenerated types for it.

Related Issues / Discussions

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QA Instructions

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Merge Plan

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Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)