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/whatwg-url/lib/encoding.js

@@ -0,0 +1,16 @@
+"use strict";
+const utf8Encoder = new TextEncoder();
+const utf8Decoder = new TextDecoder("utf-8", { ignoreBOM: true });
+
+function utf8Encode(string) {
+  return utf8Encoder.encode(string);
+}
+
+function utf8DecodeWithoutBOM(bytes) {
+  return utf8Decoder.decode(bytes);
+}
+
+module.exports = {
+  utf8Encode,
+  utf8DecodeWithoutBOM
+};