feat: theme preloading and dark mode

packages/webapp/public/preload-theme.js

@@ -0,0 +1,16 @@
+const theme =
+  localStorage.getItem('theme') ||
+  (window.matchMedia('(prefers-color-scheme: dark)').matches
+    ? 'dark'
+    : 'light');
+
+if (theme === 'dark') {
+  document.documentElement.classList.add('bp4-dark');
+  document.body.classList.add('bp4-dark');
+}
+
+// Remove dark mode for payment portal pages
+if (window.location.pathname.startsWith('/payment')) {
+  document.documentElement.classList.remove('bp4-dark');
+  document.body.classList.remove('bp4-dark');
+}