Fix: Error message: Use 'const' instead. (#13982)

### What problem does this PR solve?

Fix: Linter error message: Use 'const' instead.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Refactor**
* Updated variable declarations across form components, agent utilities,
memory management hooks, and data handling functions to enhance code
consistency and maintainability throughout the application codebase.

* **Style**
* Added ESLint suppressions to document intentional constant-condition
patterns in asynchronous event streaming operations.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

web/src/components/document-preview/ppt-preview.tsx

@@ -35,7 +35,7 @@ export const PptPreviewer: React.FC<PptPreviewerProps> = ({
           width = containerRef.current.clientWidth - 50;
           height = containerRef.current.clientHeight - 50;
         }
-        let pptxPrviewer = init(containerRef.current, {
+        const pptxPrviewer = init(containerRef.current, {
           width: width,
           height: height,
         });

web/src/components/dynamic-form.tsx

@@ -956,7 +956,7 @@ const DynamicForm = {
         onClick={() => {
           (async () => {
             try {
-              let beValid = await form.trigger();
+              const beValid = await form.trigger();
               console.log('form valid', beValid, form);
               // if (beValid) {
               //   form.handleSubmit(async (values) => {

web/src/components/floating-chat-widget-markdown.tsx

@@ -64,7 +64,7 @@ const FloatingChatWidgetMarkdown = ({
   const isDarkTheme = useIsDarkTheme();
 
   const contentWithCursor = useMemo(() => {
-    let text = content === '' ? t('chat.searching') : content;
+    const text = content === '' ? t('chat.searching') : content;
     const nextText = replaceTextByOldReg(text);
     return pipe(replaceThinkToSection, preprocessLaTeX)(nextText);
   }, [content, t]);