Security Vulnerabilities in Multivendor Admin - Username Gap and Negative Values in Restaurant Parameters

Describe the bug
When creating a new restaurant in the multivendor admin system, there are serious security vulnerabilities present. The system allows the acceptance of gaps in usernames and negative values in crucial parameters such as delivery time, minimum order, and sales tax, compromising the system's integrity.

To Reproduce
Steps to reproduce the behavior:

Log in to the multivendor admin system.
Navigate to the "Create New Restaurant" section.
Submit the form with a gap in the username field.
Observe that the system accepts the submission without displaying any error messages.
Submit the form with negative values for delivery time, minimum order, and sales tax.
Note that the system also accepts these negative values without proper validation.
Expected behavior

The system should disallow the submission of the form with gaps in the username field, displaying a clear error message.
The system should validate and reject the submission if negative values are provided for delivery time, minimum order, and sales tax, displaying appropriate error messages.
Screenshots
image

Desktop:

Browser: chrome

Start at the multivendor admin system's “Create New Restaurant” form and reproduce the username-gap and negative-value cases in Chrome. Trace the validation entry points for username, delivery time, minimum order, and sales tax; done means invalid submissions are rejected with clear error messages.

Written by the indexing model from the issue text.