fix: replace APP_DEBUG with environment-based gating

Replace the APP_DEBUG check with environment-based gating to fix issue
where boost:install command is unavailable when debug=false.

The package now only enables in 'local' and 'testing' environments,
which is more appropriate for a dev package and aligns with how other
Laravel dev tools handle environment gating.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: eduardocruz

src/BoostServiceProvider.php

@@ -55,7 +55,7 @@ public function register(): void
 
     public function boot(Router $router): void
     {
-        if (config('app.debug', false) !== true) {
+        if (! app()->environment(['local', 'testing'])) {
             return;
         }