web: checks tab unifying git, CI, deploy, PR comments, and todos

[njbrake]

Summary

Add a Checks tab per session that consolidates everything a user needs to see before shipping.

Surface

• Local git status (clean / dirty / conflicts)
• CI status for the current branch (pulled from GitHub)
• Deployment status if configured
• Unresolved PR review comments
• Outstanding user todos

Why

This information is scattered across the terminal, GitHub, and the Notes tab today. A single pre-merge readout shortens the review loop.