Enhance dashboard with key metrics, review activity, and onboarding flow

Implement new dashboard UI elements, onboarding stepper, data fetching and mutation with Tanstack Query.

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/b0f919eb-1347-4b21-b134-4f12f1c915d0.jpg