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/postcss-js/process-result.js

@@ -0,0 +1,11 @@
+let objectify = require('./objectifier')
+
+module.exports = function processResult(result) {
+  if (console && console.warn) {
+    result.warnings().forEach(warn => {
+      let source = warn.plugin || 'PostCSS'
+      console.warn(source + ': ' + warn.text)
+    })
+  }
+  return objectify(result.root)
+}