Auth: convert auth views and verification email to Nova layout

tests/Feature/Auth/UsernameAvailabilityTest.php

@@ -0,0 +1,38 @@
+<?php
+
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+it('returns available true for valid free username', function () {
+    $response = $this->getJson('/api/username/availability?username=free_name');
+
+    $response->assertOk()->assertJson([
+        'available' => true,
+        'normalized' => 'free_name',
+    ]);
+});
+
+it('returns validation error for invalid username format', function () {
+    $response = $this->getJson('/api/username/availability?username=bad.name');
+
+    $response->assertStatus(422)->assertJsonPath('available', false);
+});
+
+it('returns validation error for reserved username', function () {
+    $response = $this->getJson('/api/username/availability?username=admin');
+
+    $response->assertStatus(422)->assertJsonPath('available', false);
+});
+
+it('returns available false for already taken username', function () {
+    User::factory()->create(['username' => 'taken_name']);
+
+    $response = $this->getJson('/api/username/availability?username=taken_name');
+
+    $response->assertOk()->assertJson([
+        'available' => false,
+        'normalized' => 'taken_name',
+    ]);
+});