feat(frontend): illustrated null states and author rewards fallback

Add aksrt_get_null / widget null helpers with null.svg, use them in
sidebar widgets, comments empty, and related posts; when PM is off show
post rewards entry on the single author bar.

inc/classes/class-aksrt-widgets-new.php

@@ -107,7 +107,7 @@ class AKSRT_Hot_Posts_Widget extends WP_Widget {
             echo '</div>';
             wp_reset_postdata();
         } else {
-            echo '<p class="widget-empty">' . esc_html__('暂无热门文章', 'aksrt') . '</p>';
+            echo function_exists('aksrt_get_widget_null') ? aksrt_get_widget_null(__('暂无热门文章', 'aksrt')) : '<p class="widget-empty">' . esc_html__('暂无热门文章', 'aksrt') . '</p>';
         }
 
         echo $args['after_widget'];
@@ -360,7 +360,7 @@ class AKSRT_Tab_Posts_Widget extends WP_Widget {
                         </ul>
                         <?php endif; ?>
                     <?php else : ?>
-                        <p class="widget-empty"><?php esc_html_e('暂无文章', 'aksrt'); ?></p>
+                        <?php echo function_exists('aksrt_get_widget_null') ? aksrt_get_widget_null(__('暂无文章', 'aksrt')) : '<p class="widget-empty">' . esc_html__('暂无文章', 'aksrt') . '</p>'; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped ?>
                     <?php endif; ?>
                 </div>
             <?php wp_reset_postdata(); $first = false; endforeach; ?>