refactor(settings): always-docked editor toolbar; reorder Navigation

The 'Always show editor toolbar' preference is gone — the docked
toolbar under the file tabs is now the only mode, and the floating
hover toolbar branch in the files editor (with its open-state and
outside-click machinery) is deleted. The stored preference is dropped
by a store migration and removed from desktop settings persistence,
settings search and every locale.

Navigation section order now reads: file editor keymap, auto-save,
terminal shell + login shell, Terminal Quick Keys, and the Session
tabs group last.

packages/ui/src/lib/desktop.ts

@@ -179,7 +179,6 @@ export type DesktopSettings = {
   collapsibleUserMessages?: boolean;
   stickyUserHeader?: boolean;
   promptNavigatorEnabled?: boolean;
-  expandedEditorToolbar?: boolean;
   wideChatLayoutEnabled?: boolean;
   showSplitAssistantMessageActions?: boolean;
   fontSize?: number;