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/@babel/runtime/helpers/classApplyDescriptorSet.js

@@ -0,0 +1,7 @@
+function _classApplyDescriptorSet(e, t, l) {
+  if (t.set) t.set.call(e, l);else {
+    if (!t.writable) throw new TypeError("attempted to set read only private field");
+    t.value = l;
+  }
+}
+module.exports = _classApplyDescriptorSet, module.exports.__esModule = true, module.exports["default"] = module.exports;