Update entity and user schemas to include ID and roles

[giovannibaratta]

This change updates the /auth/info endpoint schema to return the authenticated entity's ID, associated roles, and organization role (specifically for users). It implements a discriminated union between users and agents for the GetEntityInfo200Response to safely handle the entity-specific properties.
Additionally, the /users/:id response (User schema) has been updated to include the roles property. Appropriate backend TypeScript validation models and associated test suites have been updated to ensure the changes are safely enforced.

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PR created automatically by Jules for task 6439272386163006731 started by @giovannibaratta

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