Allow individual pages/routes to be excluded from llms.txt page list

Currently, llms.txt is generated by scanning all registered routes in the app. There is no mechanism to exclude specific pages. This causes two problems: 1. Login-gated pages appear in the list because Base44's automatic exclusion only recognizes platform-level private app configuration, not app-layer auth checks using useUser(), base44.auth.me(), or custom UserContext patterns. 2. Internal/admin/diagnostic pages with registered routes (CronHealth, RoutingLogs, AdminDiagnostic, dev test pages) appear alongside public-facing pages, confusing AI crawlers about what the app actually offers users. Requested: Add a noindex_llms boolean flag (or similar) to the route configuration in pages.config.js or App.jsx Route declarations. When set, the page is excluded from llms.txt generation. This is independent of the robots.txt noindex setting. Separately, consider extending the automatic login-gated exclusion to recognize the pattern base44.auth.me() inside useQuery or useEffect at the top of a page component as equivalent to platform-level auth gating. Both changes would significantly improve llms.txt quality for production apps with mixed public/private surfaces.