add tap left/right nav in fullscreen for debugging

templates/slideshow.html

@@ -217,6 +217,10 @@
                 dx < 0 ? next() : prev();
             }
         }, { passive: true });
+        img.addEventListener('click', e => {
+            if (!document.fullscreenElement) return;
+            e.clientX < window.innerWidth / 2 ? prev() : next();
+        });
         document.addEventListener('fullscreenchange', ()=>{
             if(!document.fullscreenElement) reset_zoom();
         });