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/dlv/index.js

@@ -0,0 +1,7 @@
+export default function dlv(obj, key, def, p, undef) {
+	key = key.split ? key.split('.') : key;
+	for (p = 0; p < key.length; p++) {
+		obj = obj ? obj[key[p]] : undef;
+	}
+	return obj === undef ? def : obj;
+}