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>

tests/Feature/Api/SitesApiTest.php

@@ -0,0 +1,34 @@
+<?php
+
+use App\Models\Site;
+
+test('it lists all sites', function () {
+    Site::factory()->count(3)->create();
+
+    $response = $this->getJson('/api/sites');
+
+    $response->assertOk()->assertJsonCount(3, 'data');
+});
+
+test('it filters sites by partial name match', function () {
+    Site::factory()->create(['name' => 'My Awesome Blog']);
+    Site::factory()->create(['name' => 'Other Site']);
+
+    $response = $this->getJson('/api/sites?name=Awesome');
+
+    $response->assertOk()
+        ->assertJsonCount(1, 'data')
+        ->assertJsonPath('data.0.name', 'My Awesome Blog');
+});
+
+test('it shows a single site', function () {
+    $site = Site::factory()->create(['name' => 'Solo Site']);
+
+    $response = $this->getJson("/api/sites/{$site->id}");
+
+    $response->assertOk()->assertJsonPath('data.name', 'Solo Site');
+});
+
+test('it returns 404 for a missing site', function () {
+    $this->getJson('/api/sites/999')->assertNotFound();
+});