Add WordPress auto-update functionality (v0.6.0)

- Add UpdateController REST API endpoint for serving update info to licensed plugins
- Add PluginUpdateChecker singleton for client-side update checking
- Hook into WordPress native plugin update system (pre_set_site_transient_update_plugins, plugins_api)
- Add Auto-Updates settings subtab with enable/disable and check frequency options
- Add authentication headers for secure download requests
- Support configurable cache TTL for update checks (default 12 hours)
- Document /update-check endpoint in OpenAPI specification
- Update German translations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Plugin.php

@@ -17,6 +17,7 @@ use Jeremias\WcLicensedProduct\Admin\SettingsController;
 use Jeremias\WcLicensedProduct\Admin\VersionAdminController;
 use Jeremias\WcLicensedProduct\Api\ResponseSigner;
 use Jeremias\WcLicensedProduct\Api\RestApiController;
+use Jeremias\WcLicensedProduct\Api\UpdateController;
 use Jeremias\WcLicensedProduct\Checkout\CheckoutBlocksIntegration;
 use Jeremias\WcLicensedProduct\Checkout\CheckoutController;
 use Jeremias\WcLicensedProduct\Checkout\StoreApiExtension;
@@ -27,6 +28,7 @@ use Jeremias\WcLicensedProduct\License\LicenseManager;
 use Jeremias\WcLicensedProduct\License\PluginLicenseChecker;
 use Jeremias\WcLicensedProduct\Product\LicensedProductType;
 use Jeremias\WcLicensedProduct\Product\VersionManager;
+use Jeremias\WcLicensedProduct\Update\PluginUpdateChecker;
 use Twig\Environment;
 use Twig\Loader\FilesystemLoader;
 
@@ -139,8 +141,9 @@ final class Plugin
             new AccountController($this->twig, $this->licenseManager, $this->versionManager, $this->downloadController);
         }
 
-        // Always initialize REST API and email controller
+        // Always initialize REST API, update API, and email controller
         new RestApiController($this->licenseManager);
+        new UpdateController($this->licenseManager, $this->versionManager);
         new LicenseEmailController($this->licenseManager);
 
         // Initialize response signing if server secret is configured
@@ -162,6 +165,12 @@ final class Plugin
                 add_action('admin_notices', [$this, 'showUnlicensedNotice']);
             }
         }
+
+        // Initialize update checker if license server is configured (client-side updates)
+        $serverUrl = SettingsController::getPluginLicenseServerUrl();
+        if (!empty($serverUrl) && !$licenseChecker->isSelfLicensing()) {
+            PluginUpdateChecker::getInstance()->register();
+        }
     }
 
     /**