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/mdn-data/css/index.js

@@ -0,0 +1,8 @@
+module.exports = {
+  atRules:    require('./at-rules'),
+  selectors:  require('./selectors'),
+  types:      require('./types'),
+  properties: require('./properties'),
+  syntaxes:   require('./syntaxes'),
+  units:      require('./units'),
+}