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>

app/Http/Resources/SiteResource.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Http\Resources;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+class SiteResource extends JsonResource
+{
+    public function toArray(Request $request): array
+    {
+        return [
+            'id' => $this->id,
+            'name' => $this->name,
+            'url' => $this->url,
+            'description' => $this->description,
+            'created_at' => $this->created_at,
+            'updated_at' => $this->updated_at,
+        ];
+    }
+}