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/contains.js

@@ -0,0 +1,21 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = contains;
+
+/* eslint-disable no-bitwise, no-cond-assign */
+
+/**
+ * Checks if an element contains another given element.
+ * 
+ * @param context the context element
+ * @param node the element to check
+ */
+function contains(context, node) {
+  // HTML DOM and SVG DOM may have different support levels,
+  // so we need to check on context instead of a document root element.
+  if (context.contains) return context.contains(node);
+  if (context.compareDocumentPosition) return context === node || !!(context.compareDocumentPosition(node) & 16);
+}
+
+module.exports = exports["default"];