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/send-to-back.js

@@ -0,0 +1,18 @@
+/**
+ * @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 SendToBack = createLucideIcon("SendToBack", [
+  ["rect", { x: "14", y: "14", width: "8", height: "8", rx: "2", key: "1b0bso" }],
+  ["rect", { x: "2", y: "2", width: "8", height: "8", rx: "2", key: "1x09vl" }],
+  ["path", { d: "M7 14v1a2 2 0 0 0 2 2h1", key: "pao6x6" }],
+  ["path", { d: "M14 7h1a2 2 0 0 1 2 2v1", key: "19tdru" }]
+]);
+
+export { SendToBack as default };
+//# sourceMappingURL=send-to-back.js.map