refactor(core): upgrade to Laravel 12

[andrasbacsai]

Summary

• Migrate from legacy service providers and kernel classes to Laravel 11's unified bootstrap/app.php configuration
• Remove RouteServiceProvider, BroadcastServiceProvider, ConfigurationServiceProvider, Http\Kernel, and Console\Kernel
• Consolidate schedule configuration into new ScheduleConfiguration class
• Simplify entry points (artisan, public/index.php) using new bootstrap conventions
• Replace RouteServiceProvider::HOME references with literal '/' redirect targets
• Move middleware, exception handling, and rate limiting configuration to centralized bootstrap setup
• Update exception handler tests to work with new exception handling API

Breaking Changes

• RouteServiceProvider class no longer exists — replace any references to RouteServiceProvider::HOME with '/'
• Exception handler is now configured via bootstrap/app.php closures instead of App\Exceptions\Handler class
• Middleware configuration is now declarative in bootstrap/app.php rather than via Http\Kernel
• Console schedule configuration now uses ScheduleConfiguration class with explicit configure() method
• Broadcasting and rate limiter configuration moved from service providers to AppServiceProvider