fix: Prevent hiding settings entry in DockContextMenu

[SaKaNa-Y]

Description

If Settings gets accidentally hidden, there’s no way to show it again.

• Fix a bug where the Settings dock entry (~settings) could be hidden via the right-click context menu, with no way to
  show it again
• The Settings view is the only UI for managing dock entry visibility, so hiding it creates a dead-end
• Updated canHide() in DockContextMenu.ts to return false for the ~settings entry

Linked Issues

Additional context