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-tauri/src/lib.rs

@@ -0,0 +1,65 @@
+use tauri::{RunEvent, WindowEvent, Emitter};
+
+mod utils;
+mod commands;
+mod file_handler;
+
+use commands::{start_backend, check_backend_health, get_opened_file, clear_opened_file, cleanup_backend, set_opened_file};
+use utils::{add_log, get_tauri_logs};
+
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+  // Initialize file handler early for macOS
+  file_handler::early_init();
+  
+  tauri::Builder::default()
+    .plugin(tauri_plugin_shell::init())
+    .plugin(tauri_plugin_fs::init())
+    .setup(|app| {
+      add_log("🚀 Tauri app setup started".to_string());
+      
+      // Initialize platform-specific file handler
+      file_handler::initialize_file_handler(&app.handle());
+      
+      add_log("🔍 DEBUG: Setup completed".to_string());
+      Ok(())
+    })
+    .invoke_handler(tauri::generate_handler![start_backend, check_backend_health, get_opened_file, clear_opened_file, get_tauri_logs])
+    .build(tauri::generate_context!())
+    .expect("error while building tauri application")
+    .run(|app_handle, event| {
+      match event {
+        RunEvent::ExitRequested { .. } => {
+          add_log("🔄 App exit requested, cleaning up...".to_string());
+          cleanup_backend();
+          // Use Tauri's built-in cleanup
+          app_handle.cleanup_before_exit();
+        }
+        RunEvent::WindowEvent { event: WindowEvent::CloseRequested {.. }, .. } => {
+          add_log("🔄 Window close requested, cleaning up...".to_string());
+          cleanup_backend();
+          // Allow the window to close
+        }
+        #[cfg(target_os = "macos")]
+        RunEvent::Opened { urls } => {
+          add_log(format!("📂 Tauri file opened event: {:?}", urls));
+          for url in urls {
+            let url_str = url.as_str();
+            if url_str.starts_with("file://") {
+              let file_path = url_str.strip_prefix("file://").unwrap_or(url_str);
+              if file_path.ends_with(".pdf") {
+                add_log(format!("📂 Processing opened PDF: {}", file_path));
+                set_opened_file(file_path.to_string());
+                let _ = app_handle.emit("macos://open-file", file_path.to_string());
+              }
+            }
+          }
+        }
+        _ => {
+          // Only log unhandled events in debug mode to reduce noise
+          // #[cfg(debug_assertions)]
+          // add_log(format!("🔍 DEBUG: Unhandled event: {:?}", event));
+        }
+      }
+    });
+}