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/queue-microtask/index.js

@@ -0,0 +1,9 @@
+/*! queue-microtask. MIT License. Feross Aboukhadijeh <https://feross.org/opensource> */
+let promise
+
+module.exports = typeof queueMicrotask === 'function'
+  ? queueMicrotask.bind(typeof window !== 'undefined' ? window : global)
+  // reuse resolved promise, and allocate it lazily
+  : cb => (promise || (promise = Promise.resolve()))
+    .then(cb)
+    .catch(err => setTimeout(() => { throw err }, 0))