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/lodash/_baseAssignIn.js

@@ -0,0 +1,17 @@
+var copyObject = require('./_copyObject'),
+    keysIn = require('./keysIn');
+
+/**
+ * The base implementation of `_.assignIn` without support for multiple sources
+ * or `customizer` functions.
+ *
+ * @private
+ * @param {Object} object The destination object.
+ * @param {Object} source The source object.
+ * @returns {Object} Returns `object`.
+ */
+function baseAssignIn(object, source) {
+  return object && copyObject(source, keysIn(source), object);
+}
+
+module.exports = baseAssignIn;