Shell Pilot 1.12.1

Fixed sidebar directory tree freeze and flicker issues.

• File tree loading moved to a background queue to prevent the beachball spinner when expanding large directories
• Fixed race condition in handleCodebaseChanges that could trigger repeated reloads during filesystem events
• Replaced LazyVStack with VStack in the sidebar directory tree to eliminate layout flicker
• Restricted FileTreeWatcher to only run for explicitly pinned codebase roots, preventing unnecessary reloads
• Reduced main-actor churn by making GitService methods nonisolated