Fix the remaining crashes

This issue is to track the remaining crash reports from Sentry.

• BOLTAI-V2-5E: Mixed high-volume EXC_BAD_ACCESS bucket across AppKit/SwiftUI/WebKit UI paths, including cursor UI, window access, pasteboard, timers, and RemoteLayerTreeHost.

• BOLTAI-V2-5H: RemoteLayerTreeHost/WebKit layer-tree crash, usually “failed to find layer with ID”, affecting both older macOS and macOS 26.

• BOLTAI-V2-88: EXC_BAD_ACCESS around app keyboard shortcut / command handling, culprit points to BoltAIApp.setupKeyboardShortcuts.

• BOLTAI-V2-5W: Fatal breakpoint while fetching custom provider models in AIServiceModelFetcher.fetchCustomModels.