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/viewer/CustomSearchLayer.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect, useMemo } from 'react';
+import { useState, useEffect, useMemo } from 'react';
 import { useSearch } from '@embedpdf/plugin-search/react';
 import { useViewer } from '../../contexts/ViewerContext';
 import { SEARCH_CONSTANTS } from './constants/search';
@@ -24,9 +24,9 @@ interface SearchResultState {
   activeResultIndex?: number;
 }
 
-export function CustomSearchLayer({ 
-  pageIndex, 
-  scale, 
+export function CustomSearchLayer({
+  pageIndex,
+  scale,
   highlightColor = SEARCH_CONSTANTS.HIGHLIGHT_COLORS.BACKGROUND,
   activeHighlightColor = SEARCH_CONSTANTS.HIGHLIGHT_COLORS.ACTIVE_BACKGROUND,
   opacity = SEARCH_CONSTANTS.HIGHLIGHT_COLORS.OPACITY,
@@ -42,17 +42,17 @@ export function CustomSearchLayer({
     if (!searchProvides) {
       return;
     }
-    
+
     const unsubscribe = searchProvides.onSearchResultStateChange?.((state: SearchResultState) => {
       // Auto-scroll to active search result
       if (state?.results && state.activeResultIndex !== undefined && state.activeResultIndex >= 0) {
         const activeResult = state.results[state.activeResultIndex];
-        if (activeResult) {            
+        if (activeResult) {
           const pageNumber = activeResult.pageIndex + 1; // Convert to 1-based page number
           scrollActions.scrollToPage(pageNumber);
         }
       }
-      
+
       setSearchResultState(state);
     });
 
@@ -69,7 +69,7 @@ export function CustomSearchLayer({
     const filtered = searchResultState.results
       .map((result, originalIndex) => ({ result, originalIndex }))
       .filter(({ result }) => result.pageIndex === pageIndex);
-    
+
     return filtered;
   }, [searchResultState, pageIndex]);
 
@@ -78,7 +78,7 @@ export function CustomSearchLayer({
   }
 
   return (
-    <div style={{ 
+    <div style={{
       position: 'absolute',
       top: 0,
       left: 0,
@@ -117,4 +117,4 @@ export function CustomSearchLayer({
       ))}
     </div>
   );
-}
+}

frontend/src/components/viewer/LocalEmbedPDFWithAnnotations.tsx

@@ -1,4 +1,4 @@
-import React, { useEffect, useMemo, useState } from 'react';
+import { useEffect, useMemo, useState } from 'react';
 import { createPluginRegistration } from '@embedpdf/core';
 import { EmbedPDF } from '@embedpdf/core/react';
 import { usePdfiumEngine } from '@embedpdf/engines/react';
@@ -312,4 +312,4 @@ export function LocalEmbedPDFWithAnnotations({
       </EmbedPDF>
     </div>
   );
-}
+}

frontend/src/components/viewer/PdfViewerToolbar.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react';
+import { useState, useEffect } from 'react';
 import { Button, Paper, Group, NumberInput } from '@mantine/core';
 import { useTranslation } from 'react-i18next';
 import { useViewer } from '../../contexts/ViewerContext';
@@ -14,11 +14,11 @@ interface PdfViewerToolbarProps {
   currentPage?: number;
   totalPages?: number;
   onPageChange?: (page: number) => void;
-  
+
   // Dual page toggle (placeholder for now)
   dualPage?: boolean;
   onDualPageToggle?: () => void;
-  
+
   // Zoom controls (connected via ViewerContext)
   currentZoom?: number;
 }
@@ -33,7 +33,7 @@ export function PdfViewerToolbar({
 }: PdfViewerToolbarProps) {
   const { t } = useTranslation();
   const { getScrollState, getZoomState, scrollActions, zoomActions, registerImmediateZoomUpdate, registerImmediateScrollUpdate } = useViewer();
-  
+
   const scrollState = getScrollState();
   const zoomState = getZoomState();
   const [pageInput, setPageInput] = useState(scrollState.currentPage || currentPage);
@@ -151,7 +151,7 @@ export function PdfViewerToolbar({
             input: { width: 48, textAlign: "center", fontWeight: 500, fontSize: 16 },
           }}
         />
-        
+
         <span style={{ fontWeight: 500, fontSize: 16 }}>
           / {scrollState.totalPages}
         </span>
@@ -229,4 +229,4 @@ export function PdfViewerToolbar({
         </Group>
       </Paper>
   );
-}
+}

frontend/src/components/viewer/ThumbnailSidebar.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react';
+import { useState, useEffect } from 'react';
 import { Box, ScrollArea } from '@mantine/core';
 import { useViewer } from '../../contexts/ViewerContext';
 

frontend/src/components/viewer/Viewer.tsx

@@ -1,4 +1,3 @@
-import React from 'react';
 import EmbedPdfViewer from './EmbedPdfViewer';
 
 export interface ViewerProps {
@@ -13,4 +12,4 @@ const Viewer = (props: ViewerProps) => {
   return <EmbedPdfViewer {...props} />;
 };
 
-export default Viewer;
+export default Viewer;