fix(app): polish workspace navigation surfaces

Use mobile action sheets and long-press file menus while preserving provider context across sheet portals. Keep sidebar and file-pane glyphs on shared visual rails, avoid scrollbar layout shifts, and hide keyboard affordances where shortcuts are unavailable.

packages/app/src/components/sidebar/workspace-trailing/index.tsx

@@ -62,7 +62,7 @@ export function SidebarWorkspaceTrailingContent({
 function WorkspaceTimestamp({ enteredAt }: { enteredAt: Date }) {
   const label = useCompactTimeAgo(enteredAt);
   return (
-    <Text style={styles.timestamp} numberOfLines={1}>
+    <Text style={styles.timestamp} numberOfLines={1} testID="sidebar-workspace-timestamp">
       {label}
     </Text>
   );