Improve dashboard appearance with clear stats and actionable insights

Replace simple dashboard page with a new UI using Radix primitives in `App.tsx`.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: d5daeb82-020f-4ea2-a54f-9097efac2a63
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/4119c42c-9857-448a-8c94-20be047485ba/8c9f3290-fd0a-4864-a2b9-30e87cfd81aa.jpg