Prevent boost:update from failing when there is nothing to update

[ohnotnow]

Currently boost:update needs configured agents before it checks whether there is anything to update, so an MCP-only setup (php artisan boost:install --mcp) gets Please set up Boost with [php artisan boost:install] first. and a non-zero exit code.

This PR reorders the checks in handle() so that when guidelines or skills aren't configured the command exits successfully before requiring the agents part.

Example run that shows the current behaviour in a new project that this PR (seems to!) fix:

$ composer require --dev laravel/boost
... <all fine>

$ php artisan boost:install --mcp
... <all looks ok>

$ php artisan boost:update
Please set up Boost with [php artisan boost:install] first.

[pushpak1300]

Thanks