feat: render Settings in a windowed dialog

- Open Settings as a centered windowed dialog on desktop with a blurred backdrop
- Update SettingsView to support windowed mode and adjust Mac titlebar padding for windowed use
- Export SettingsWindow and switch MainLayout to use it instead of full-screen overlay

packages/ui/src/components/views/index.ts

@@ -5,3 +5,4 @@ export { DiffView, useDiffFileCount } from './DiffView';
 export { TerminalView } from './TerminalView';
 export { FilesView } from './FilesView';
 export { SettingsView } from './SettingsView';
+export { SettingsWindow } from './SettingsWindow';