refactor(frontend): remove unused React default imports (#4529)

## Description of Changes

- Removed unused `React` default imports across multiple frontend
components.
- Updated imports to only include required React hooks and types (e.g.,
`useState`, `useEffect`, `Suspense`, `createContext`).
- Ensured consistency with React 17+ JSX transform, where default
`React` import is no longer required.
- This cleanup reduces bundle size slightly and aligns code with modern
React best practices.

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

Co-authored-by: Reece Browne <74901996+reecebrowne@users.noreply.github.com>

frontend/src/components/shared/FilePickerModal.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react';
+import { useState, useEffect } from 'react';
 import {
   Modal,
   Text,

frontend/src/components/shared/FileUploadButton.tsx

@@ -1,4 +1,4 @@
-import React, { useRef } from "react";
+import { useRef } from "react";
 import { FileButton, Button } from "@mantine/core";
 import { useTranslation } from "react-i18next";
 

frontend/src/components/shared/Footer.tsx

@@ -1,5 +1,4 @@
 import { Flex } from '@mantine/core';
-import React from 'react';
 import { useTranslation } from 'react-i18next';
 import { useCookieConsent } from '../../hooks/useCookieConsent';
 

frontend/src/components/shared/MultiSelectControls.tsx

@@ -1,4 +1,3 @@
-import React from "react";
 import { Box, Group, Text, Button } from "@mantine/core";
 import { useTranslation } from "react-i18next";
 
@@ -37,7 +36,7 @@ const MultiSelectControls = ({
           >
             {t("fileManager.clearSelection", "Clear Selection")}
           </Button>
-          
+
           {onAddToUpload && (
             <Button
               size="xs"
@@ -47,7 +46,7 @@ const MultiSelectControls = ({
               {t("fileManager.addToUpload", "Add to Upload")}
             </Button>
           )}
-          
+
           {onOpenInFileEditor && (
             <Button
               size="xs"
@@ -58,7 +57,7 @@ const MultiSelectControls = ({
               {t("fileManager.openInFileEditor", "Open in File Editor")}
             </Button>
           )}
-          
+
           {onOpenInPageEditor && (
             <Button
               size="xs"
@@ -69,7 +68,7 @@ const MultiSelectControls = ({
               {t("fileManager.openInPageEditor", "Open in Page Editor")}
             </Button>
           )}
-          
+
           {onDeleteAll && (
             <Button
               size="xs"
@@ -85,4 +84,4 @@ const MultiSelectControls = ({
   );
 };
 
-export default MultiSelectControls;
+export default MultiSelectControls;

frontend/src/components/shared/NavigationWarningModal.tsx

@@ -1,4 +1,3 @@
-import React from 'react';
 import { Modal, Text, Button, Group, Stack } from '@mantine/core';
 import { useNavigationGuard } from '../../contexts/NavigationContext';
 import { useTranslation } from 'react-i18next';

frontend/src/components/shared/RainbowThemeProvider.tsx

@@ -1,4 +1,4 @@
-import React, { createContext, useContext, ReactNode } from 'react';
+import { createContext, useContext, ReactNode } from 'react';
 import { MantineProvider } from '@mantine/core';
 import { useRainbowTheme } from '../../hooks/useRainbowTheme';
 import { mantineTheme } from '../../theme/mantineTheme';