Enable ESLint no-unused-vars rule (#4367)

# Description of Changes
Enable ESLint [no-unused-vars
rule](https://typescript-eslint.io/rules/no-unused-vars/)

frontend/src/components/viewer/Viewer.tsx

@@ -1,19 +1,17 @@
 import React, { useEffect, useState, useRef, useCallback } from "react";
-import { Paper, Stack, Text, ScrollArea, Loader, Center, Button, Group, NumberInput, useMantineTheme, ActionIcon, Box, Tabs } from "@mantine/core";
+import { Paper, Stack, Text, ScrollArea, Center, Button, Group, NumberInput, useMantineTheme, ActionIcon, Box, Tabs } from "@mantine/core";
 import { useTranslation } from "react-i18next";
 import { pdfWorkerManager } from "../../services/pdfWorkerManager";
 import ArrowBackIosNewIcon from "@mui/icons-material/ArrowBackIosNew";
 import ArrowForwardIosIcon from "@mui/icons-material/ArrowForwardIos";
 import FirstPageIcon from "@mui/icons-material/FirstPage";
 import LastPageIcon from "@mui/icons-material/LastPage";
-import ViewSidebarIcon from "@mui/icons-material/ViewSidebar";
 import ViewWeekIcon from "@mui/icons-material/ViewWeek"; // for dual page (book)
 import DescriptionIcon from "@mui/icons-material/Description"; // for single page
 import CloseIcon from "@mui/icons-material/Close";
-import { useLocalStorage } from "@mantine/hooks";
 import { fileStorage } from "../../services/fileStorage";
 import SkeletonLoader from '../shared/SkeletonLoader';
-import { useFileState, useFileActions, useCurrentFile } from "../../contexts/FileContext";
+import { useFileState } from "../../contexts/FileContext";
 import { useFileWithUrl } from "../../hooks/useFileWithUrl";
 import { isFileObject } from "../../types/fileContext";
 import { FileId } from "../../types/file";
@@ -142,8 +140,6 @@ export interface ViewerProps {
 }
 
 const Viewer = ({
-  sidebarsVisible,
-  setSidebarsVisible,
   onClose,
   previewFile,
 }: ViewerProps) => {
@@ -152,13 +148,7 @@ const Viewer = ({
 
   // Get current file from FileContext
   const { selectors } = useFileState();
-  const { actions } = useFileActions();
-  const currentFile = useCurrentFile();
 
-  const getCurrentFile = () => currentFile.file;
-  const getCurrentProcessedFile = () => currentFile.record?.processedFile || undefined;
-  const clearAllFiles = actions.clearAllFiles;
-  const addFiles = actions.addFiles;
   const activeFiles = selectors.getFiles();
 
   // Tab management for multiple files
@@ -406,7 +396,7 @@ const Viewer = ({
           // Start progressive preloading after a short delay
           setTimeout(() => startProgressivePreload(), 100);
         }
-      } catch (error) {
+      } catch {
         if (!cancelled) {
           setPageImages([]);
           setNumPages(0);