Updates an area identified by externalCode in the URL.

Business Rules:

• name: Required. Maximum 300 characters.
• externalCode: Required. Maximum 50 characters. Must be unique within the company (must not match another area's code).
• similarity: Required. Must be a valid area similarity value.
• description: Optional. Maximum 900 characters.
• organizationUnit: Optional. If provided, identify the department by uuid and/or externalCode (at least one). If both are sent, uuid is used for lookup.
• costCenter: Optional. If provided, identify the cost center by uuid and/or externalCode (at least one). If both are sent, uuid is used for lookup.

Validation:

• All required fields must be provided and not empty.
• The area identified by externalCode in the URL must exist for the company.

Errors (HTTP):

• 404 when no area matches the URL externalCode for the company.
• 422 when a nested cost center or organization unit reference cannot be resolved.
• 500 for any other unexpected failure (generic Internal server error response).