feat(schema): add SPDX license enum to license field

[teneplaysofficial]

PR Checklist

• The PR title follows
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Description

This PR updates the JSON Schema to enhance the license field by adding:

• A full SPDX-compliant enum list of valid license identifiers.
• A default license value of "MIT".

Reason

To standardize license metadata across packages and ensure a consistent default when none is specified.

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