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/resolve/lib/is-core.js

@@ -0,0 +1,5 @@
+var isCoreModule = require('is-core-module');
+
+module.exports = function isCore(x) {
+    return isCoreModule(x);
+};