Chat-list PR-state icon stale after merge — stays green/Open until manual refresh

Summary

In the chat list sidebar, each session has a small repo-shaped icon that's coloured green when the associated PR is open and purple when the PR is merged (matching GitHub's standard PR-state colours). The icon doesn't update after the PR's state changes on GitHub — a chat whose PR has been merged continues to show as green/Open until something forces a refresh.

Reproduction

1. Open a Claude Code chat in a worktree where you've just opened a PR. Icon: green / "Open" — correct.
2. Merge the PR on github.com (squash, merge, or rebase — happens for all merge types).
3. Return to the Claude Code chat list. Icon: still green / "Open". Click the chat's "View PR" button on the status row → opens the PR in browser, which clearly shows purple / Merged.

So the truth is on GitHub, the chat list cache is stale.

Expected

The icon should track the PR state with reasonable freshness — either pull on chat-list focus, on tab/app focus, or on an interval.

Workaround

None known. Restart Claude Code? (untested)

Context

• Discovered on macOS desktop Claude Code, 2026-05-10.
• Related observation: the icon-state semantics (green = open, purple = merged) don't appear to be documented anywhere — I checked the changelog and docs before posting. Worth documenting alongside the fix.