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/toPairsIn.js

@@ -0,0 +1,30 @@
+var createToPairs = require('./_createToPairs'),
+    keysIn = require('./keysIn');
+
+/**
+ * Creates an array of own and inherited enumerable string keyed-value pairs
+ * for `object` which can be consumed by `_.fromPairs`. If `object` is a map
+ * or set, its entries are returned.
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @alias entriesIn
+ * @category Object
+ * @param {Object} object The object to query.
+ * @returns {Array} Returns the key-value pairs.
+ * @example
+ *
+ * function Foo() {
+ *   this.a = 1;
+ *   this.b = 2;
+ * }
+ *
+ * Foo.prototype.c = 3;
+ *
+ * _.toPairsIn(new Foo);
+ * // => [['a', 1], ['b', 2], ['c', 3]] (iteration order is not guaranteed)
+ */
+var toPairsIn = createToPairs(keysIn);
+
+module.exports = toPairsIn;