fix(toc): restore correct floating TOC positioning after layout refactor

Fix incorrect TOC alignment caused by outdated DOM selector in toc.js.
The content reference element changed during layout refactor, breaking
position calculations for the floating TOC.

Updated contentColumn selector to use .main-wrapper/.container fallback,
ensuring correct left offset and responsive positioning.

Also adds a more robust fallback chain to prevent future regressions
when layout structure changes.

single.php

@@ -17,7 +17,9 @@ $show_hide_related_posts = get_theme_mod(
 <div id="primary" class="inside-page content-area">
     <div class="container">
         <div class="main-wrapper">
-
+            
+            <?php zeitfresser_render_floating_toc(); ?>
+            
             <section class="page-section full-width-view">
                 <div class="detail-content">