feat: add prefix option for authentication routes

[dimtrovich]

Description

This pull request adds the ability to prefix all authentication route paths using a new prefix option in the routes() method.

• New prefix option: Allows you to define a common prefix for all authentication routes (default /)
• Refactoring: Replaces the hard-coded route group ‘/’ with a configurable $prefix variable

Benefits of this change

• Increased flexibility - Allows you to group auth routes under a single prefix (e.g., auth/login, auth/register)
• Better organization - Facilitates the organization of routes in complex applications
• Consistency - Complements the existing namespace and except options
• Backward compatible - The default value / preserves the existing behavior

Usage example

// All routes will be prefixed with ‘auth’
service(‘auth’)->routes($routes, [‘prefix’ => ‘auth’]);

// Generates: auth/login, auth/register, auth/logout, etc.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

This makes sense. However, could we rename prefix to group? It would better align with the underlying method we use.