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/dom-helpers/cjs/isWindow.js

@@ -0,0 +1,16 @@
+"use strict";
+
+var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
+
+exports.__esModule = true;
+exports.default = isWindow;
+
+var _isDocument = _interopRequireDefault(require("./isDocument"));
+
+function isWindow(node) {
+  if ('window' in node && node.window === node) return node;
+  if ((0, _isDocument.default)(node)) return node.defaultView || false;
+  return false;
+}
+
+module.exports = exports["default"];