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/side-channel/index.d.ts

@@ -0,0 +1,14 @@
+import getSideChannelList from 'side-channel-list';
+import getSideChannelMap from 'side-channel-map';
+import getSideChannelWeakMap from 'side-channel-weakmap';
+
+declare namespace getSideChannel {
+	type Channel<K, V> =
+		| getSideChannelList.Channel<K, V>
+		| ReturnType<Exclude<typeof getSideChannelMap<K, V>, false>>
+		| ReturnType<Exclude<typeof getSideChannelWeakMap<K, V>, false>>;
+}
+
+declare function getSideChannel<K, V>(): getSideChannel.Channel<K, V>;
+
+export = getSideChannel;