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/add.js

@@ -0,0 +1,22 @@
+var createMathOperation = require('./_createMathOperation');
+
+/**
+ * Adds two numbers.
+ *
+ * @static
+ * @memberOf _
+ * @since 3.4.0
+ * @category Math
+ * @param {number} augend The first number in an addition.
+ * @param {number} addend The second number in an addition.
+ * @returns {number} Returns the total.
+ * @example
+ *
+ * _.add(6, 4);
+ * // => 10
+ */
+var add = createMathOperation(function(augend, addend) {
+  return augend + addend;
+}, 0);
+
+module.exports = add;