fix(desktop): DeerFlow UI — ChatArea refactor + ai-elements + dead CSS cleanup

ChatArea retry button uses setInput instead of direct sendToGateway,
fix bootstrap spinner stuck for non-logged-in users,
remove dead CSS (aurora-title/sidebar-open/quick-action-chips),
add ai components (ReasoningBlock/StreamingText/ChatMode/ModelSelector/TaskProgress),
add ClassroomPlayer + ResizableChatLayout + artifact panel

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/lib/kernel-chat.ts

@@ -103,6 +103,12 @@ export function installChatMethods(ClientClass: { prototype: KernelClient }): vo
             callbacks.onDelta(streamEvent.delta);
             break;
 
+          case 'thinkingDelta':
+            if (callbacks.onThinkingDelta) {
+              callbacks.onThinkingDelta(streamEvent.delta);
+            }
+            break;
+
           case 'tool_start':
             log.debug('Tool started:', streamEvent.name, streamEvent.input);
             if (callbacks.onTool) {