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/ownerWindow.js

@@ -0,0 +1,20 @@
+"use strict";
+
+var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
+
+exports.__esModule = true;
+exports.default = ownerWindow;
+
+var _ownerDocument = _interopRequireDefault(require("./ownerDocument"));
+
+/**
+ * Returns the owner window of a given element.
+ * 
+ * @param node the element
+ */
+function ownerWindow(node) {
+  var doc = (0, _ownerDocument.default)(node);
+  return doc && doc.defaultView || window;
+}
+
+module.exports = exports["default"];