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/getComputedStyle.js

@@ -0,0 +1,11 @@
+import ownerWindow from './ownerWindow';
+/**
+ * Returns one or all computed style properties of an element.
+ * 
+ * @param node the element
+ * @param psuedoElement the style property
+ */
+
+export default function getComputedStyle(node, psuedoElement) {
+  return ownerWindow(node).getComputedStyle(node, psuedoElement);
+}