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/diff.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 Diff = createLucideIcon("Diff", [
+  ["path", { d: "M12 3v14", key: "7cf3v8" }],
+  ["path", { d: "M5 10h14", key: "elsbfy" }],
+  ["path", { d: "M5 21h14", key: "11awu3" }]
+]);
+
+export { Diff as default };
+//# sourceMappingURL=diff.js.map