ci: regenerate JSON schema during release

[Hweinstock]

Description

The release workflow does not regenerate schemas/agentcore.schema.v1.json from the Zod source schemas. If schema changes are merged between releases, the published JSON schema file can drift from the actual validation logic.

This adds a schema regeneration step to the prepare-release job, after the version bump and before the release branch commit. The existing git add -A picks up the regenerated file automatically.

Related Issue

Closes #

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe): CI workflow improvement

Testing

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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