Persist pull request identity and sidebar status

[jln13x]

Summary

• Persist canonical pull request associations on threads created from or updated with a known pull request.
• Refresh explicit associations by provider, repository-qualified URL, and pull request number, while retaining last-known status as stale when provider refreshes fail.
• Keep explicit PR status visible when a thread has no branch or local repository; inferred PRs still require an exact checked-out branch match.
• Share explicit refreshes by canonical PR identity across worktrees instead of polling independently per checkout.
• Protect background provider polling with a sustained 30-request/minute budget, a 10-request burst, and at most four concurrent provider calls.
• Cache open PR state for one minute, closed state for five minutes, and merged state for fifteen minutes; provider failures back off exponentially up to fifteen minutes.
• Keep the compact sidebar treatment: open is green, merged is purple, closed is muted gray, and threads without a known pull request have no icon.
• Cover persistence, projection, migration, refresh fallback, web, and mobile flows behind the durable change-request-status feature flag.

Sidebar preview

Regression review

• Feature-flag-off behavior remains branch-bound and does not render persisted associations.
• GitHub durable refreshes derive the repository from the canonical PR URL, so an unrelated checkout with the same PR number cannot populate the shared entry.
• Provider errors and exhausted polling budgets retain last-known state as stale instead of clearing the icon.
• Stale inferred results are keyed to the branch that produced them, so switching branches cannot carry the old PR icon forward.
• Multi-selector branch discovery reserves its worst-case GitHub API cost, including repository-context resolution.
• Persisted provider terminology remains correct while live provider metadata is unavailable or unrelated.
• Visible rows share one web hook and subscription policy; branchless threads without repository context render stored state without starting a poller.

Validation

• 116 focused tests across shared resolution, polling policy, GitHub lookup, Git manager, and broadcaster behavior
• vp check
• vp run typecheck
• vp run lint:mobile