feat: add read-only Sites API

Add GET /api/sites endpoint for listing sites with optional name filter,
and GET /api/sites/{site} for showing individual sites. Includes API
resource, controller, routes registration, and comprehensive tests.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bootstrap/app.php

@@ -8,6 +8,7 @@ use Illuminate\Http\Request;
 return Application::configure(basePath: dirname(__DIR__))
     ->withRouting(
         web: __DIR__.'/../routes/web.php',
+        api: __DIR__.'/../routes/api.php',
         commands: __DIR__.'/../routes/console.php',
         health: '/up',
     )