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/d3-timer/src/timeout.js

@@ -0,0 +1,11 @@
+import {Timer} from "./timer.js";
+
+export default function(callback, delay, time) {
+  var t = new Timer;
+  delay = delay == null ? 0 : +delay;
+  t.restart(elapsed => {
+    t.stop();
+    callback(elapsed + delay);
+  }, delay, time);
+  return t;
+}