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-weakmap/index.d.ts

@@ -0,0 +1,15 @@
+declare namespace getSideChannelWeakMap {
+	type Channel<K, V> = {
+		assert: (key: K) => void;
+		has: (key: K) => boolean;
+		get: (key: K) => V | undefined;
+		set: (key: K, value: V) => void;
+		delete: (key: K) => boolean;
+	}
+}
+
+declare function getSideChannelWeakMap<K, V>(): getSideChannelWeakMap.Channel<K, V>;
+
+declare const x: false | typeof getSideChannelWeakMap;
+
+export = x;