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>

languages/wc-licensed-product.pot

@@ -6,9 +6,9 @@
 #, fuzzy
 msgid ""
 msgstr ""
-"Project-Id-Version: WC Licensed Product 0.5.12\n"
+"Project-Id-Version: WC Licensed Product 0.6.0\n"
 "Report-Msgid-Bugs-To: magdev3.0@gmail.com\n"
-"POT-Creation-Date: 2026-01-27 14:41+0100\n"
+"POT-Creation-Date: 2026-01-27 18:00+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1869,3 +1869,47 @@ msgstr ""
 #: wc-licensed-product.php:119
 msgid "WC Licensed Product requires WooCommerce to be installed and active."
 msgstr ""
+
+#: src/Api/UpdateController.php:175
+msgid "License validation failed."
+msgstr ""
+
+#: src/Api/UpdateController.php:185
+msgid "License not found."
+msgstr ""
+
+#: src/Api/UpdateController.php:195
+msgid "Licensed product not found."
+msgstr ""
+
+#: src/Api/UpdateController.php:207
+msgid "No versions available for this product."
+msgstr ""
+
+#: src/Update/PluginUpdateChecker.php:295
+msgid "WooCommerce plugin for selling licensed software products with domain-bound license keys."
+msgstr ""
+
+#: src/Admin/SettingsController.php:163
+msgid "Auto-Updates"
+msgstr ""
+
+#: src/Admin/SettingsController.php:165
+msgid "Configure automatic plugin updates from the license server."
+msgstr ""
+
+#: src/Admin/SettingsController.php:169
+msgid "Enable Auto-Updates"
+msgstr ""
+
+#: src/Admin/SettingsController.php:172
+msgid "Automatically check for and receive plugin updates from the license server."
+msgstr ""
+
+#: src/Admin/SettingsController.php:177
+msgid "Check Frequency (Hours)"
+msgstr ""
+
+#: src/Admin/SettingsController.php:180
+msgid "How often to check for updates (in hours)."
+msgstr ""