feat(ui): add swipe gesture to open/close sidebar on mobile

Swipe right from the left edge (30px zone) opens the sidebar,
swipe left when open closes it. Ignores vertical scrolling.

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

ui/src/components/Layout.tsx

@@ -80,6 +80,51 @@ export function Layout() {
     setMobileNavVisible(true);
   }, [isMobile]);
 
+  // Swipe gesture to open/close sidebar on mobile
+  useEffect(() => {
+    if (!isMobile) return;
+
+    const EDGE_ZONE = 30; // px from left edge to start open-swipe
+    const MIN_DISTANCE = 50; // minimum horizontal swipe distance
+    const MAX_VERTICAL = 75; // max vertical drift before we ignore
+
+    let startX = 0;
+    let startY = 0;
+
+    const onTouchStart = (e: TouchEvent) => {
+      const t = e.touches[0]!;
+      startX = t.clientX;
+      startY = t.clientY;
+    };
+
+    const onTouchEnd = (e: TouchEvent) => {
+      const t = e.changedTouches[0]!;
+      const dx = t.clientX - startX;
+      const dy = Math.abs(t.clientY - startY);
+
+      if (dy > MAX_VERTICAL) return; // vertical scroll, ignore
+
+      // Swipe right from left edge → open
+      if (!sidebarOpen && startX < EDGE_ZONE && dx > MIN_DISTANCE) {
+        setSidebarOpen(true);
+        return;
+      }
+
+      // Swipe left when open → close
+      if (sidebarOpen && dx < -MIN_DISTANCE) {
+        setSidebarOpen(false);
+      }
+    };
+
+    document.addEventListener("touchstart", onTouchStart, { passive: true });
+    document.addEventListener("touchend", onTouchEnd, { passive: true });
+
+    return () => {
+      document.removeEventListener("touchstart", onTouchStart);
+      document.removeEventListener("touchend", onTouchEnd);
+    };
+  }, [isMobile, sidebarOpen, setSidebarOpen]);
+
   const handleMainScroll = useCallback(
     (event: UIEvent<HTMLElement>) => {
       if (!isMobile) return;