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/css-tree/lib/syntax/atrule/nest.js

@@ -0,0 +1,12 @@
+export default {
+    parse: {
+        prelude() {
+            return this.createSingleNodeList(
+                this.SelectorList()
+            );
+        },
+        block() {
+            return this.Block(true);
+        }
+    }
+};