Update a user

Updates a user's information.

Allowed fields:

• Nome: User's full name
• email: User's email address
• contact_number: Phone number
• username: Login username
• superior: ID of the user's manager
• pontodevenda: Point of sale ID (reassign POS)
• website_photo_url: Profile photo URL
• website_role: Role displayed on website
• website_description: Bio/description for website
• website_visible: Whether visible on website (bit)

Payroll fields (written to the linked Cliente row, not Utilizadores; a client is created + linked lazily if the user doesn't have one yet):

• nif: Tax ID (int; blank clears it)
• iban: Salary IBAN ("IBAN Vencimento")
• iban_alimentar: Food-allowance IBAN ("IBAN Alimentação")