Fix guide content language and language switcher context

- Change getGuidePage() to use currentLanguage instead of detectLanguage()
- Add lang_switch_url template variable for proper context-aware switching
- Language switcher now stays on guide page when switching languages
- Guide content now displays in correct language based on URL parameter

engine/core/class/CodePressCMS.php

@@ -626,7 +626,7 @@ class CodePressCMS {
      * @return array Guide page data
      */
     private function getGuidePage() {
-        $lang = $this->detectLanguage();
+        $lang = $this->currentLanguage;
         $guideFile = __DIR__ . '/../../../guide/' . $lang . '.md';
         
         if (!file_exists($guideFile)) {
@@ -796,6 +796,8 @@ class CodePressCMS {
             'homepage_title' => $homepageTitle,
             'is_homepage' => (!isset($_GET['page']) || $_GET['page'] === $this->config['default_page']),
             'home_active_class' => (!isset($_GET['page']) || $_GET['page'] === $this->config['default_page']) ? 'active' : '',
+            'is_guide_page' => isset($_GET['guide']),
+            'lang_switch_url' => isset($_GET['guide']) ? '&guide' : '&page=' . $this->config['default_page'],
             'author_name' => $this->config['author']['name'] ?? 'CodePress Developer',
             'author_website' => $this->config['author']['website'] ?? '#',
             'author_git' => $this->config['author']['git'] ?? '#',