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/lucide-react/dist/esm/icons/split-square-vertical.js

@@ -0,0 +1,17 @@
+/**
+ * @license lucide-react v0.303.0 - ISC
+ *
+ * This source code is licensed under the ISC license.
+ * See the LICENSE file in the root directory of this source tree.
+ */
+
+import createLucideIcon from '../createLucideIcon.js';
+
+const SplitSquareVertical = createLucideIcon("SplitSquareVertical", [
+  ["path", { d: "M5 8V5c0-1 1-2 2-2h10c1 0 2 1 2 2v3", key: "1pi83i" }],
+  ["path", { d: "M19 16v3c0 1-1 2-2 2H7c-1 0-2-1-2-2v-3", key: "ido5k7" }],
+  ["line", { x1: "4", x2: "20", y1: "12", y2: "12", key: "1e0a9i" }]
+]);
+
+export { SplitSquareVertical as default };
+//# sourceMappingURL=split-square-vertical.js.map