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/security-index.ts

@@ -47,7 +47,6 @@ export type { EncryptedData } from './crypto-utils';
 // Re-export secure storage
 export {
   secureStorage,
-  secureStorageSync,
   isSecureStorageAvailable,
   storeDeviceKeys,
   getDeviceKeys,