fix: Block shortcode rendering during page template loading

- Added $loading_page_template flag in TemplateLoader
- template-wrapper.php sets flag before loading theme header/footer
- Shortcodes::render_template() returns early if flag is set
- Prevents recursion from theme components, widgets, or other plugins

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

includes/Frontend/Shortcodes.php

@@ -552,6 +552,12 @@ class Shortcodes {
      * @return string
      */
     private function render_template( string $template, array $context ): string {
+        // Block shortcode rendering while loading page template to prevent recursion.
+        // This catches any shortcodes triggered by theme header/footer, widgets, etc.
+        if ( TemplateLoader::is_loading_page_template() ) {
+            return '<!-- FediStream: shortcode blocked during page template loading -->';
+        }
+
         // Check for unlicensed mode.
         if ( $this->unlicensed_mode ) {
             return $this->get_unlicensed_message();