V2 Tauri integration (#3854)

# Description of Changes

Please provide a summary of the changes, including:

## Add PDF File Association Support for Tauri App

  ### 🎯 **Features Added**
  - PDF file association configuration in Tauri
  - Command line argument detection for opened files
  - Automatic file loading when app is launched via "Open with"
  - Cross-platform support (Windows/macOS)

  ### 🔧 **Technical Changes**
  - Added `fileAssociations` in `tauri.conf.json` for PDF files
  - New `get_opened_file` Tauri command to detect file arguments
  - `fileOpenService` with Tauri fs plugin integration
  - `useOpenedFile` hook for React integration
  - Improved backend health logging during startup (reduced noise)

  ### 🧪 **Testing**
See 
* https://v2.tauri.app/start/prerequisites/
*
[DesktopApplicationDevelopmentGuide.md](DesktopApplicationDevelopmentGuide.md)

  ```bash
  # Test file association during development:
  
  cd frontend
  npm install
  cargo tauri dev --no-watch -- -- "path/to/file.pdf"
  ```

 For production testing:
  1. Build: npm run tauri build
  2. Install the built app
  3. Right-click PDF → "Open with" → Stirling-PDF

  🚀 User Experience

- Users can now double-click PDF files to open them directly in
Stirling-PDF
- Files automatically load in the viewer when opened via file
association
  - Seamless integration with OS file handling

---

## 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/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/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/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/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Connor Yoh <[email protected]>
Co-authored-by: James Brunton <[email protected]>
Co-authored-by: James Brunton <[email protected]>

frontend/src/desktop/services/fileOpenService.ts

@@ -0,0 +1,147 @@
+import { invoke, isTauri } from '@tauri-apps/api/core';
+
+export interface FileOpenService {
+  getOpenedFile(): Promise<string | null>;
+  readFileAsArrayBuffer(filePath: string): Promise<{ fileName: string; arrayBuffer: ArrayBuffer } | null>;
+  clearOpenedFile(): Promise<void>;
+  onFileOpened(callback: (filePath: string) => void): () => void; // Returns unlisten function
+}
+
+class TauriFileOpenService implements FileOpenService {
+  async getOpenedFile(): Promise<string | null> {
+    try {
+      console.log('🔍 Calling invoke(get_opened_file)...');
+      const result = await invoke<string | null>('get_opened_file');
+      console.log('🔍 invoke(get_opened_file) returned:', result);
+      return result;
+    } catch (error) {
+      console.error('❌ Failed to get opened file:', error);
+      return null;
+    }
+  }
+
+  async readFileAsArrayBuffer(filePath: string): Promise<{ fileName: string; arrayBuffer: ArrayBuffer } | null> {
+    try {
+      const { readFile } = await import('@tauri-apps/plugin-fs');
+
+      const fileData = await readFile(filePath);
+      const fileName = filePath.split(/[\\/]/).pop() || 'opened-file.pdf';
+
+      return {
+        fileName,
+        arrayBuffer: fileData.buffer.slice(fileData.byteOffset, fileData.byteOffset + fileData.byteLength)
+      };
+    } catch (error) {
+      console.error('Failed to read file:', error);
+      return null;
+    }
+  }
+
+  async clearOpenedFile(): Promise<void> {
+    try {
+      console.log('🔍 Calling invoke(clear_opened_file)...');
+      await invoke('clear_opened_file');
+      console.log('✅ Successfully cleared opened file');
+    } catch (error) {
+      console.error('❌ Failed to clear opened file:', error);
+    }
+  }
+
+  onFileOpened(callback: (filePath: string) => void): () => void {
+    let cleanup: (() => void) | null = null;
+    let isCleanedUp = false;
+
+    const setupEventListeners = async () => {
+      try {
+        // Check if already cleaned up before async setup completes
+        if (isCleanedUp) {
+          return;
+        }
+
+        // Only import if in Tauri environment
+        if (isTauri()) {
+          const { listen } = await import('@tauri-apps/api/event');
+
+          // Check again after async import
+          if (isCleanedUp) {
+            return;
+          }
+
+          // Listen for macOS native file open events
+          const unlistenMacOS = await listen('macos://open-file', (event) => {
+            console.log('📂 macOS native file open event:', event.payload);
+            callback(event.payload as string);
+          });
+
+          // Listen for fallback file open events
+          const unlistenFallback = await listen('file-opened', (event) => {
+            console.log('📂 Fallback file open event:', event.payload);
+            callback(event.payload as string);
+          });
+
+          // Set up cleanup function only if not already cleaned up
+          if (!isCleanedUp) {
+            cleanup = () => {
+              try {
+                unlistenMacOS();
+                unlistenFallback();
+                console.log('✅ File event listeners cleaned up');
+              } catch (error) {
+                console.error('❌ Error during file event cleanup:', error);
+              }
+            };
+          } else {
+            // Clean up immediately if cleanup was called during setup
+            try {
+              unlistenMacOS();
+              unlistenFallback();
+            } catch (error) {
+              console.error('❌ Error during immediate cleanup:', error);
+            }
+          }
+        }
+      } catch (error) {
+        console.error('❌ Failed to setup file event listeners:', error);
+      }
+    };
+
+    setupEventListeners();
+
+    // Return cleanup function
+    return () => {
+      isCleanedUp = true;
+      if (cleanup) {
+        cleanup();
+      }
+    };
+  }
+}
+
+class WebFileOpenService implements FileOpenService {
+  async getOpenedFile(): Promise<string | null> {
+    // In web mode, there's no file association support
+    return null;
+  }
+
+  async readFileAsArrayBuffer(_filePath: string): Promise<{ fileName: string; arrayBuffer: ArrayBuffer } | null> {
+    // In web mode, cannot read arbitrary file paths
+    return null;
+  }
+
+  async clearOpenedFile(): Promise<void> {
+    // In web mode, no file clearing needed
+  }
+
+  onFileOpened(_callback: (filePath: string) => void): () => void {
+    // In web mode, no file events - return no-op cleanup function
+    console.log('ℹ️ Web mode: File event listeners not supported');
+    return () => {
+      // No-op cleanup for web mode
+    };
+  }
+}
+
+// Export the appropriate service based on environment
+export const fileOpenService: FileOpenService = isTauri()
+  ? new TauriFileOpenService()
+  : new WebFileOpenService();