tui: hide header when sidebar is visible and window is narrow to maximize content area

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -887,7 +887,7 @@ export function Session() {
       <box flexDirection="row">
         <box flexGrow={1} paddingBottom={1} paddingTop={1} paddingLeft={2} paddingRight={2} gap={1}>
           <Show when={session()}>
-            <Show when={!sidebarVisible()}>
+            <Show when={!sidebarVisible() || !wide()}>
               <Header />
             </Show>
             <scrollbox