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/removeClass.js

@@ -0,0 +1,20 @@
+function replaceClassName(origClass, classToRemove) {
+  return origClass.replace(new RegExp("(^|\\s)" + classToRemove + "(?:\\s|$)", 'g'), '$1').replace(/\s+/g, ' ').replace(/^\s*|\s*$/g, '');
+}
+/**
+ * Removes a CSS class from a given element.
+ * 
+ * @param element the element
+ * @param className the CSS class name
+ */
+
+
+export default function removeClass(element, className) {
+  if (element.classList) {
+    element.classList.remove(className);
+  } else if (typeof element.className === 'string') {
+    element.className = replaceClassName(element.className, className);
+  } else {
+    element.setAttribute('class', replaceClassName(element.className && element.className.baseVal || '', className));
+  }
+}