feat(KAN-16): add English localization foundation

tests/Feature/LocalizationTest.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Support\Facades\Validator;
+use Inertia\Testing\AssertableInertia as Assert;
+use Symfony\Component\Process\Process;
+use Tests\TestCase;
+
+class LocalizationTest extends TestCase
+{
+    public function test_frontend_localization_behaviour(): void
+    {
+        $process = new Process(['node', 'tests/Fixtures/localization.mjs'], base_path());
+        $process->setTimeout(60);
+        $process->run();
+
+        $this->assertTrue($process->isSuccessful(), $process->getOutput().$process->getErrorOutput());
+        $this->assertStringContainsString('Localization behavior checks passed.', $process->getOutput());
+    }
+
+    public function test_initial_page_shares_the_application_locale_and_time_zone(): void
+    {
+        config(['app.timezone' => 'Europe/Berlin']);
+
+        $this->withHeader('Accept-Language', 'de-DE')->get(route('home'))
+            ->assertOk()
+            ->assertSee('lang="en"', false)
+            ->assertInertia(fn (Assert $page) => $page
+                ->where('localization.locale', 'en')
+                ->where('localization.timeZone', 'Europe/Berlin'));
+    }
+
+    public function test_server_validation_remains_english(): void
+    {
+        $this->assertSame('en', config('app.locale'));
+        $this->assertSame('en', config('app.fallback_locale'));
+
+        $validator = Validator::make(['email' => 'invalid'], [
+            'title' => ['required'],
+            'email' => ['email'],
+        ]);
+
+        $this->assertSame('The title field is required.', $validator->errors()->first('title'));
+        $this->assertSame('The email field must be a valid email address.', $validator->errors()->first('email'));
+    }
+}