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/siginfo/index.js

@@ -0,0 +1,20 @@
+module.exports = function (query, force) {
+  var isAttached = false
+  if (process.stderr.isTTY || force === true) {
+    isAttached = true
+    process.on('SIGINFO', onsiginfo)
+    process.on('SIGUSR1', onsiginfo)
+  }
+
+  return function () {
+    if (isAttached === true) {
+      process.removeListener('SIGINFO', onsiginfo)
+      process.removeListener('SIGUSR1', onsiginfo)
+      isAttached = false
+    }
+  }
+
+  function onsiginfo () {
+    query()
+  }
+}