fix: rework compact nav and centralized back routing

Use master-detail layout on skinny windows so server and channel lists share one screen, with back returning to the space list instead of redirect loops. Add useBackRoute for title-bar and page-header back buttons with view transitions.

src/app/components/title-bar/TitleBar.css.ts

@@ -76,6 +76,11 @@ export const TitleBarDragRegion = style({
   color: color.Surface.OnContainer,
 });
 
+export const TitleBarBackButton = style({
+  WebkitAppRegion: 'no-drag',
+  flexShrink: 0,
+});
+
 export const SyncStatusBadge = style({
   position: 'absolute',
   left: '50%',