[OPIK-6013] [FE] fix: CSV upload overlay stuck when server-side processing enabled (#6330)

Skip showing the CsvUploadDialog overlay when isCsvUploadEnabled is true,
since the upload is handled server-side in the background and a toast already
confirms acceptance. Previously the overlay showed "Upload in progress..." with
no close button and was never dismissed because the sidebar stays open for the
success step (unlike the old dialog flow which closed entirely).

Also add a visually-hidden DialogTitle to CsvUploadDialog for accessibility.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: itamargolan

apps/opik-frontend/src/v2/pages-shared/datasets/AddEditDatasetDialog/useDatasetForm.ts

@@ -254,7 +254,7 @@ const useDatasetForm = ({
         ? () => onCreateSuccess(newDataset, navigateToDataset)
         : navigateToDataset;
 
-      if (hasValidCsvFile) {
+      if (hasValidCsvFile && !isCsvUploadEnabled) {
         setIsOverlayShown(true);
       }
 
@@ -271,6 +271,7 @@ const useDatasetForm = ({
       applyEvaluationCriteria,
       uploadItems,
       hasValidCsvFile,
+      isCsvUploadEnabled,
       onDatasetCreated,
       onCreateSuccess,
       setOpen,

apps/opik-frontend/src/v2/pages-shared/datasets/CsvUploadDialog/CsvUploadDialog.tsx

@@ -1,6 +1,6 @@
 import React from "react";
 import { Button } from "@/ui/button";
-import { Dialog, DialogContent } from "@/ui/dialog";
+import { Dialog, DialogContent, DialogTitle } from "@/ui/dialog";
 import Loader from "@/shared/Loader/Loader";
 
 type CsvUploadDialogProps = {
@@ -17,6 +17,9 @@ const CsvUploadDialog: React.FC<CsvUploadDialogProps> = ({
   return (
     <Dialog open={open}>
       <DialogContent className="max-w-sm [&>button.absolute]:hidden">
+        <DialogTitle className="sr-only">
+          {isCsvMode ? "Upload in progress" : "Processing CSV"}
+        </DialogTitle>
         <Loader
           className="min-h-40"
           message={