Tidy Tauri code and enable "Open file in Stirling PDF" (#4836)

# Description of Changes
Tidy Tauri code and enable "Open file in Stirling PDF"

frontend/src/desktop/hooks/useAppInitialization.ts

@@ -0,0 +1,47 @@
+import { useEffect } from 'react';
+import { useBackendInitializer } from '@app/hooks/useBackendInitializer';
+import { useOpenedFile } from '@app/hooks/useOpenedFile';
+import { fileOpenService } from '@app/services/fileOpenService';
+import { useFileManagement } from '@app/contexts/file/fileHooks';
+
+/**
+ * App initialization hook
+ * Desktop version: Handles Tauri-specific initialization
+ * - Starts the backend on app startup
+ * - Handles files opened with the app (adds directly to FileContext)
+ */
+export function useAppInitialization(): void {
+  // Initialize backend on app startup
+  useBackendInitializer();
+
+  // Get file management actions
+  const { addFiles } = useFileManagement();
+
+  // Handle file opened with app (Tauri mode)
+  const { openedFilePath, loading: openedFileLoading } = useOpenedFile();
+
+  // Load opened file and add directly to FileContext
+  useEffect(() => {
+    if (openedFilePath && !openedFileLoading) {
+      const loadOpenedFile = async () => {
+        try {
+          const fileData = await fileOpenService.readFileAsArrayBuffer(openedFilePath);
+          if (fileData) {
+            // Create a File object from the ArrayBuffer
+            const file = new File([fileData.arrayBuffer], fileData.fileName, {
+              type: 'application/pdf'
+            });
+
+            // Add directly to FileContext
+            await addFiles([file]);
+            console.log('[Desktop] Opened file added to FileContext:', fileData.fileName);
+          }
+        } catch (error) {
+          console.error('[Desktop] Failed to load opened file:', error);
+        }
+      };
+
+      loadOpenedFile();
+    }
+  }, [openedFilePath, openedFileLoading, addFiles]);
+}