fix(ui): show panel toggle button in all modes (not just non-compact)

desktop/src/components/ChatArea.tsx

@@ -361,13 +361,11 @@ export function ChatArea({ compact, onOpenDetail }: { compact?: boolean; onOpenD
               <Search className="w-3.5 h-3.5" />
             </Button>
           )}
-          {/* Side panel toggle — Trae Solo style, in header */}
+          {/* Side panel toggle — Trae Solo style, always in header */}
-          {!compact && (
           <PanelToggleButton
             panelOpen={artifactPanelOpen}
             onToggle={() => setArtifactPanelOpen(!artifactPanelOpen)}
           />
-          )}
           {/* 详情按钮 (简洁模式) */}
           {compact && onOpenDetail && (
             <Button