Enforce type checking in CI (#4126)

# Description of Changes
Currently, the `tsconfig.json` file enforces strict type checking, but
nothing in CI checks that the code is actually correctly typed. [Vite
only transpiles TypeScript
code](https://vite.dev/guide/features.html#transpile-only) so doesn't
ensure that the TS code we're running is correct.

This PR adds running of the type checker to CI and fixes the type errors
that have already crept into the codebase.

Note that many of the changes I've made to 'fix the types' are just
using `any` to disable the type checker because the code is under too
much churn to fix anything properly at the moment. I still think
enabling the type checker now is the best course of action though
because otherwise we'll never be able to fix all of them, and it should
at least help us not break things when adding new code.

Co-authored-by: James <james@crosscourtanalytics.com>

frontend/src/components/viewer/Viewer.tsx

@@ -137,7 +137,7 @@ export interface ViewerProps {
   sidebarsVisible: boolean;
   setSidebarsVisible: (v: boolean) => void;
   onClose?: () => void;
-  previewFile?: File; // For preview mode - bypasses context
+  previewFile: File | null; // For preview mode - bypasses context
 }
 
 const Viewer = ({
@@ -148,18 +148,13 @@ const Viewer = ({
 }: ViewerProps) => {
   const { t } = useTranslation();
   const theme = useMantineTheme();
-  
+
   // Get current file from FileContext
   const { getCurrentFile, getCurrentProcessedFile, clearAllFiles, addFiles, activeFiles } = useFileContext();
-  const currentFile = getCurrentFile();
-  const processedFile = getCurrentProcessedFile();
-  
-  // Convert File to FileWithUrl format for viewer
-  const pdfFile = useFileWithUrl(currentFile);
-  
+
   // Tab management for multiple files
   const [activeTab, setActiveTab] = useState<string>("0");
-  
+
   // Reset PDF state when switching tabs
   const handleTabChange = (newTab: string) => {
     setActiveTab(newTab);
@@ -183,7 +178,7 @@ const Viewer = ({
   const file2WithUrl = useFileWithUrl(activeFiles[2]);
   const file3WithUrl = useFileWithUrl(activeFiles[3]);
   const file4WithUrl = useFileWithUrl(activeFiles[4]);
-  
+
   const filesWithUrls = React.useMemo(() => {
     return [file0WithUrl, file1WithUrl, file2WithUrl, file3WithUrl, file4WithUrl]
       .slice(0, activeFiles.length)
@@ -197,11 +192,11 @@ const Viewer = ({
       if (!(previewFile instanceof File)) {
         return null;
       }
-      
+
       if (previewFile.size === 0) {
         return null;
       }
-      
+
       return { file: previewFile, url: null };
     } else {
       // Use the file from the active tab
@@ -262,12 +257,12 @@ const Viewer = ({
   // Progressive preloading function
   const startProgressivePreload = async () => {
     if (!pdfDocRef.current || preloadingRef.current || numPages === 0) return;
-    
+
     preloadingRef.current = true;
-    
+
     // Start with first few pages for immediate viewing
     const priorityPages = [0, 1, 2, 3, 4]; // First 5 pages
-    
+
     // Render priority pages first
     for (const pageIndex of priorityPages) {
       if (pageIndex < numPages && !pageImages[pageIndex]) {
@@ -276,7 +271,7 @@ const Viewer = ({
         await new Promise(resolve => setTimeout(resolve, 50));
       }
     }
-    
+
     // Then render remaining pages in background
     for (let pageIndex = 5; pageIndex < numPages; pageIndex++) {
       if (!pageImages[pageIndex]) {
@@ -285,7 +280,7 @@ const Viewer = ({
         await new Promise(resolve => setTimeout(resolve, 100));
       }
     }
-    
+
     preloadingRef.current = false;
   };
 
@@ -300,15 +295,15 @@ const Viewer = ({
   const scrollToPage = (pageNumber: number) => {
     const el = pageRefs.current[pageNumber - 1];
     const scrollArea = scrollAreaRef.current;
-    
+
     if (el && scrollArea) {
       const scrollAreaRect = scrollArea.getBoundingClientRect();
       const elRect = el.getBoundingClientRect();
       const currentScrollTop = scrollArea.scrollTop;
-      
+
       // Position page near top of viewport with some padding
       const targetScrollTop = currentScrollTop + (elRect.top - scrollAreaRect.top) - 20;
-      
+
       scrollArea.scrollTo({
         top: targetScrollTop,
         behavior: "smooth"
@@ -364,7 +359,7 @@ const Viewer = ({
       setLoading(true);
       try {
         let pdfData;
-        
+
         // For preview files, use ArrayBuffer directly to avoid blob URL issues
         if (previewFile && effectiveFile.file === previewFile) {
           const arrayBuffer = await previewFile.arrayBuffer();
@@ -446,7 +441,7 @@ const Viewer = ({
           <CloseIcon />
         </ActionIcon>
       )}
-      
+
       {!effectiveFile ? (
         <Center style={{ flex: 1 }}>
           <Text c="red">Error: No file provided to viewer</Text>
@@ -455,8 +450,8 @@ const Viewer = ({
         <>
           {/* Tabs for multiple files */}
           {activeFiles.length > 1 && !previewFile && (
-            <Box 
-              style={{ 
+            <Box
+              style={{
                 borderBottom: '1px solid var(--mantine-color-gray-3)',
                 backgroundColor: 'var(--mantine-color-body)',
                 position: 'relative',
@@ -475,7 +470,7 @@ const Viewer = ({
               </Tabs>
             </Box>
           )}
-          
+
           {loading ? (
             <div style={{ flex: 1, padding: '1rem' }}>
               <SkeletonLoader type="viewer" />