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/width.js

@@ -0,0 +1,23 @@
+"use strict";
+
+var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
+
+exports.__esModule = true;
+exports.default = getWidth;
+
+var _isWindow = _interopRequireDefault(require("./isWindow"));
+
+var _offset = _interopRequireDefault(require("./offset"));
+
+/**
+ * Returns the width of a given element.
+ * 
+ * @param node the element
+ * @param client whether to use `clientWidth` if possible
+ */
+function getWidth(node, client) {
+  var win = (0, _isWindow.default)(node);
+  return win ? win.innerWidth : client ? node.clientWidth : (0, _offset.default)(node).width;
+}
+
+module.exports = exports["default"];