Problem The moment two agents' branches collide is exactly when SproutGit should shine; today users must drop to a terminal or external merge tool.

Proposal Minimal three-pane conflict view in the existing Monaco editor (ours / theirs / result), with per-conflict accept buttons.

Priority: P2 — table stakes. From the triage in docs/improvement-ideas.md (https://github.com/InterestingSoftware/SproutGit/blob/main/docs/improvement-ideas.md).