refactor context menu and keyboard navigation handling for improved clarity and maintainability

dicom-viewer/src/App.tsx

@@ -1174,7 +1174,7 @@ function App({ container_id, imageStacks, autoCacheStack, annotationJson, viewer
     };
   }, []);
 
-useEffect(() => {
+  useEffect(() => {
     const el = appRootRef.current;
     if (!el) return;
     const handleContextMenu = (e: MouseEvent) => {
@@ -1184,7 +1184,7 @@ useEffect(() => {
     return () => {
       el.removeEventListener("contextmenu", handleContextMenu);
     };
-}, []);
+  }, []);
 
   useEffect(() => {
     if (!referenceLinesEnabled) return;
@@ -1926,6 +1926,8 @@ useEffect(() => {
 
 
   useEffect(() => {
+    const el = appRootRef.current;
+    if (!el) return;
     function handleArrowKeyNavigation(e: KeyboardEvent) {
       console.log("Handling arrow key navigation", e.key);
       console.log("activeViewport", activeViewport);
@@ -1975,8 +1977,11 @@ useEffect(() => {
       }
     }
 
-    window.addEventListener("keydown", handleArrowKeyNavigation);
+    el.addEventListener("keydown", handleArrowKeyNavigation);
-    return () => window.removeEventListener("keydown", handleArrowKeyNavigation);
+
+    return () => {
+      el.removeEventListener("keydown", handleArrowKeyNavigation);
+    };
   }, [activeViewport, viewportModes, viewportImageIds, updateOverlay]);
 
 
@@ -2401,7 +2406,7 @@ useEffect(() => {
         </div>
 
         {/* Preset menu (bottom right of viewport) */}
-<div
+        <div
           style={{
             position: "absolute",
             right: 8,
@@ -2409,7 +2414,7 @@ useEffect(() => {
             zIndex: 10,
             pointerEvents: "auto", // <-- ensure pointer events are enabled
           }}
->
+        >
           <div
             className="preset-menu"
             style={{
@@ -2492,7 +2497,7 @@ useEffect(() => {
               </div>
             )}
           </div>
-</div>
+        </div>
         {/* Position bar inside each viewport */}
         {viewportModes[i] === "stack" && viewportImageIds[i] && (
           <div