IA-835: Fix validation issues in user creation form in compte parent

Description

This MR fixes validation behavior in the user creation form:

First Name & Last Name:

Removed default values

Required validation message appears correctly

Prevents numeric input

Email:

Removed default value

Proper invalid email validation

Prevents incorrect email format

Phone Number:

Removed default value

Displays invalid number message

Allows full deletion

Prevents invalid formats

Fixed mismatch between phone country and parent app country