feat(image-zoom): implement multi-touch pinch detection for zoom functionality

- Added support for pinch gestures to enhance the zoom experience on touch devices.
- Implemented event listeners for pointer events to manage pinch start and end.
- Updated closing behavior to account for active pinch gestures, improving user interaction.

assets/js/image-zoom.js

@@ -23,12 +23,42 @@
 
     overlay.appendChild(img);
 
+    // Track pinch gesture
+    let pinching = false;
+    let pinchTimer = 0;
+    const activeTouchPointers = new Set();
+    function pinchingStart() {
+      pinching = true;
+      if (pinchTimer) clearTimeout(pinchTimer);
+    }
+    function pinchingEndSoon() {
+      if (pinchTimer) clearTimeout(pinchTimer);
+      pinchTimer = setTimeout(() => (pinching = false), 350);
+    }
+    function onPointerDown(e) {
+      if (e.pointerType === 'touch') {
+        activeTouchPointers.add(e.pointerId);
+        if (activeTouchPointers.size > 1) pinchingStart();
+      }
+    }
+    function onPointerUp(e) {
+      if (e.pointerType === 'touch') {
+        activeTouchPointers.delete(e.pointerId);
+        if (activeTouchPointers.size < 2) pinchingEndSoon();
+      }
+    }
+
     function close(immediate = false) {
       // trigger dedicated closing transitions for smoother zoom-out
       overlay.classList.add("closing");
       window.removeEventListener("keydown", onKeyDown, true);
       window.removeEventListener("scroll", onScroll, true);
       overlay.removeEventListener("wheel", onWheel);
+      overlay.removeEventListener("pointerdown", onPointerDown);
+      overlay.removeEventListener("pointerup", onPointerUp);
+      overlay.removeEventListener("pointercancel", onPointerUp);
+      activeTouchPointers.clear();
+      if (pinchTimer) clearTimeout(pinchTimer);
 
       if (immediate) {
         overlay.remove();
@@ -44,10 +74,21 @@
     overlay.addEventListener("click", () => close(false), { once: true });
     window.addEventListener("keydown", onKeyDown, true);
 
-    function onWheel(e) { if (e && e.ctrlKey) return; close(true); }
-    function onScroll() { close(true); }
+    function onWheel(e) {
+      // Ignore trackpad pinch (wheel + ctrlKey) and active pinch
+      if ((e && e.ctrlKey) || pinching) return;
+      close(true);
+    }
+    function onScroll() {
+      if (pinching) return;
+      close(true);
+    }
 
     overlay.addEventListener("wheel", onWheel, { passive: true });
+    // Standard W3C pointer events for multi-touch pinch detection
+    overlay.addEventListener("pointerdown", onPointerDown);
+    overlay.addEventListener("pointerup", onPointerUp);
+    overlay.addEventListener("pointercancel", onPointerUp);
     window.addEventListener("scroll", onScroll, true);
 
     document.body.appendChild(overlay);