Fix pinch-to-zoom being misinterpreted as swipe navigation

Multi-finger gestures like pinch-to-zoom were triggering photo
navigation because the touch handler didn't check touch count.
Move swipe detection to touchend, reject multi-touch gestures,
and require a minimum 40px horizontal distance.

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

public/js/photonav.js

@@ -30,21 +30,38 @@ function disableKeyDownPropagation(obj) {
 function enableTouchNavigation() {
 	var x_down = null;
 	var y_down = null;
+	var cancelled = false;
 
 	document.addEventListener('touchstart', function(event) {
+		if (event.touches.length > 1) {
+			cancelled = true;
+			return;
+		}
 		x_down = event.touches[0].clientX;
 		y_down = event.touches[0].clientY;
+		cancelled = false;
 	}, false);
 
 	document.addEventListener('touchmove', function(event) {
-		if (!x_down || !y_down) {
+		if (event.touches.length > 1) {
+			cancelled = true;
+		}
+	}, false);
+
+	document.addEventListener('touchend', function(event) {
+		if (cancelled || x_down === null || y_down === null) {
+			x_down = null;
+			y_down = null;
 			return;
 		}
 
-		var x_diff = x_down - event.touches[0].clientX;
+		var x_diff = x_down - event.changedTouches[0].clientX;
-		var y_diff = y_down - event.touches[0].clientY;
+		var y_diff = y_down - event.changedTouches[0].clientY;
 
-		if (Math.abs(y_diff) > 50) {
+		x_down = null;
+		y_down = null;
+
+		if (Math.abs(x_diff) < 40 || Math.abs(y_diff) > 50) {
 			return;
 		}
 
@@ -52,13 +69,11 @@ function enableTouchNavigation() {
 			if (x_diff > 0) {
 				var target = document.getElementById("previous_photo").href;
 				if (target) {
-					event.preventDefault();
 					document.location.href = target + '#photo_frame';
 				}
 			} else {
 				var target = document.getElementById("next_photo").href;
 				if (target) {
-					event.preventDefault();
 					document.location.href = target + '#photo_frame';
 				}
 			}