Move auto-update settings from Mobile App page to Settings page

- Relocate update section (version check, repo config, token) to Settings
- Fix download URL for private repos: append Gitea auth token
- Mobile App page now only has FCM/notification settings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/class-twp-auto-updater.php

@@ -210,6 +210,12 @@ class TWP_Auto_Updater {
             $download_url = $release->zipball_url;
         }
 
+        // Append auth token to download URL for private repos
+        if (!empty($gitea_token) && $download_url) {
+            $separator = (strpos($download_url, '?') !== false) ? '&' : '?';
+            $download_url .= $separator . 'token=' . urlencode($gitea_token);
+        }
+
         // Format changelog
         $changelog = !empty($release->body) ? $release->body : 'No changelog provided for this release.';