feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/node_modules/dom-helpers/esm/getScrollAccessor.js

@@ -0,0 +1,20 @@
+import isWindow from './isWindow';
+export default function getscrollAccessor(offset) {
+  var prop = offset === 'pageXOffset' ? 'scrollLeft' : 'scrollTop';
+
+  function scrollAccessor(node, val) {
+    var win = isWindow(node);
+
+    if (val === undefined) {
+      return win ? win[offset] : node[prop];
+    }
+
+    if (win) {
+      win.scrollTo(win[offset], val);
+    } else {
+      node[prop] = val;
+    }
+  }
+
+  return scrollAccessor;
+}