style: lighter inline code, black system bars for the installed app

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/public/manifest.json

@@ -6,8 +6,8 @@
   "start_url": "/",
   "scope": "/",
   "display": "standalone",
-  "background_color": "#2563eb",
-  "theme_color": "#2563eb",
+  "background_color": "#000000",
+  "theme_color": "#000000",
   "orientation": "portrait-primary",
   "icons": [
     {