[BUG] "Pull request status couldn't be checked" banner persistently appears on every session in worktree branches without an associated PR

Description

A red warning banner displaying "Pull request status couldn't be checked and may be out of date" appears in the top-right corner of every Claude Code session that is associated with a worktree branch which has no open Pull Request on GitHub.

Reproduction

1. Open Claude Code with multiple sessions, each tied to its own worktree branch (created automatically by Claude Code).
2. Do not create a PR for those branches (or close any PRs that existed).
3. The banner appears at the top-right of every session.
4. Dismissing it via the ✕ icon only hides it temporarily — it reappears the next time the session is opened (or on the next status refresh).

Expected behavior

• If no PR exists for the branch, the banner should not appear at all, OR
• A user-facing setting should exist to disable PR status checking on worktree sessions.

Actual behavior

• Banner appears persistently on all sessions, regardless of whether the branch has any commits or any PR.
• No setting in the documented settings.json schema controls this banner.

Environment

• Claude Code on Windows 11
• Multiple worktree-based sessions in the same repository
• Branches with no associated PR (some empty, some with commits)

Impact

Pure visual noise — does not block work, but is persistently distracting across many sessions.