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/axios/lib/helpers/toURLEncodedForm.js

@@ -0,0 +1,19 @@
+'use strict';
+
+import utils from '../utils.js';
+import toFormData from './toFormData.js';
+import platform from '../platform/index.js';
+
+export default function toURLEncodedForm(data, options) {
+  return toFormData(data, new platform.classes.URLSearchParams(), {
+    visitor: function (value, key, path, helpers) {
+      if (platform.isNode && utils.isBuffer(value)) {
+        this.append(key, value.toString('base64'));
+        return false;
+      }
+
+      return helpers.defaultVisitor.apply(this, arguments);
+    },
+    ...options,
+  });
+}