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/tauriBackendService.ts

@@ -0,0 +1,61 @@
+import { invoke } from '@tauri-apps/api/core';
+
+export class TauriBackendService {
+  private static instance: TauriBackendService;
+  private backendStarted = false;
+
+  static getInstance(): TauriBackendService {
+    if (!TauriBackendService.instance) {
+      TauriBackendService.instance = new TauriBackendService();
+    }
+    return TauriBackendService.instance;
+  }
+
+  isBackendRunning(): boolean {
+    return this.backendStarted;
+  }
+
+  async startBackend(backendUrl?: string): Promise<void> {
+    if (this.backendStarted) {
+      return;
+    }
+
+    try {
+      const result = await invoke('start_backend', { backendUrl });
+      console.log('Backend started:', result);
+      this.backendStarted = true;
+      
+      // Wait for backend to be healthy
+      await this.waitForHealthy();
+    } catch (error) {
+      console.error('Failed to start backend:', error);
+      throw error;
+    }
+  }
+
+  async checkBackendHealth(): Promise<boolean> {
+    if (!this.backendStarted) {
+      return false;
+    }
+    try {
+      return await invoke('check_backend_health');
+    } catch (error) {
+      console.error('Health check failed:', error);
+      return false;
+    }
+  }
+
+  private async waitForHealthy(maxAttempts = 60): Promise<void> {
+    for (let i = 0; i < maxAttempts; i++) {
+      const isHealthy = await this.checkBackendHealth();
+      if (isHealthy) {
+        console.log('Backend is healthy');
+        return;
+      }
+      await new Promise(resolve => setTimeout(resolve, 1000));
+    }
+    throw new Error('Backend failed to become healthy after 60 seconds');
+  }
+}
+
+export const tauriBackendService = TauriBackendService.getInstance();