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/async.js

@@ -0,0 +1,15 @@
+let postcss = require('postcss')
+
+let parse = require('./parser')
+let processResult = require('./process-result')
+
+module.exports = function async(plugins) {
+  let processor = postcss(plugins)
+  return async input => {
+    let result = await processor.process(input, {
+      parser: parse,
+      from: undefined
+    })
+    return processResult(result)
+  }
+}