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/extends.js

@@ -0,0 +1,10 @@
+function _extends() {
+  return module.exports = _extends = Object.assign ? Object.assign.bind() : function (n) {
+    for (var e = 1; e < arguments.length; e++) {
+      var t = arguments[e];
+      for (var r in t) ({}).hasOwnProperty.call(t, r) && (n[r] = t[r]);
+    }
+    return n;
+  }, module.exports.__esModule = true, module.exports["default"] = module.exports, _extends.apply(null, arguments);
+}
+module.exports = _extends, module.exports.__esModule = true, module.exports["default"] = module.exports;