Implement optimistic UI for file uploads and enhance message handling (#967)

* feat(upload): implement optimistic UI for file uploads and enhance message handling

* feat(middleware): enhance file handling by collecting historical uploads from directory

* feat(thread-title): update page title handling for new threads and improve loading state

* feat(uploads-middleware): enhance file extraction by verifying file existence in uploads directory

* feat(thread-stream): update file path reference to use virtual_path for uploads

* feat(tests): add core behaviour tests for UploadsMiddleware

* feat(tests): remove unused pytest import from test_uploads_middleware_core_logic.py

* feat: enhance file upload handling and localization support

- Update UploadsMiddleware to validate filenames more robustly.
- Modify MessageListItem to parse uploaded files from raw content for backward compatibility.
- Add localization for uploading messages in English and Chinese.
- Introduce parseUploadedFiles utility to extract uploaded files from message content.

frontend/src/components/workspace/thread-title.tsx

@@ -4,6 +4,7 @@ import { useEffect } from "react";
 import { useI18n } from "@/core/i18n/hooks";
 import type { AgentThreadState } from "@/core/threads";
 
+import { useThreadChat } from "./chats";
 import { FlipDisplay } from "./flip-display";
 
 export function ThreadTitle({
@@ -15,8 +16,9 @@ export function ThreadTitle({
   thread: BaseStream<AgentThreadState>;
 }) {
   const { t } = useI18n();
+  const { isNewThread } = useThreadChat();
   useEffect(() => {
-    const pageTitle = !thread.values
+    const pageTitle = isNewThread
       ? t.pages.newChat
       : thread.values?.title && thread.values.title !== "Untitled"
         ? thread.values.title
@@ -27,6 +29,7 @@ export function ThreadTitle({
       document.title = `${pageTitle} - ${t.pages.appName}`;
     }
   }, [
+    isNewThread,
     t.pages.newChat,
     t.pages.untitled,
     t.pages.appName,