Creates a new role (cargo) for the company resolved from the API token.

Business rules:

• name, externalCode, and similarity are required.
• externalCode must be unique among active roles for the same company.
• jobLevel is optional: omit the field, send null, or send an empty string ("")—empty string is normalized to null before persistence.
• description is optional: omit the field, send null, or send an empty string.

Validation:

• Invalid enum values for similarity or jobLevel, or other constraint violations return 400 with validation details.