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/rrweb-cssom/lib/StyleSheet.js

@@ -0,0 +1,17 @@
+//.CommonJS
+var CSSOM = {};
+///CommonJS
+
+
+/**
+ * @constructor
+ * @see http://dev.w3.org/csswg/cssom/#the-stylesheet-interface
+ */
+CSSOM.StyleSheet = function StyleSheet() {
+	this.parentStyleSheet = null;
+};
+
+
+//.CommonJS
+exports.StyleSheet = CSSOM.StyleSheet;
+///CommonJS