Create high scores and agent stats tab

[areibman]

Add a "High Scores" tab to provide engineering managers with key performance metrics for both human and AI agent contributors.

This tab includes team performance metrics (e.g., merge rate, average merge time, code velocity), a dedicated section for AI agent performance (PRs raised vs. merged), and a leaderboard for top contributors.

---

 

Fixes #170

[cursor[bot]]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch. _{Learn more about Cursor Agents}