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/hooks/useBackendHealth.ts

@@ -0,0 +1,91 @@
+import { useState, useEffect, useCallback } from 'react';
+import { tauriBackendService } from '@app/services/tauriBackendService';
+
+export type BackendStatus = 'starting' | 'healthy' | 'unhealthy' | 'stopped';
+
+interface BackendHealthState {
+  status: BackendStatus;
+  message?: string;
+  lastChecked?: number;
+  isChecking: boolean;
+  error: string | null;
+}
+
+/**
+ * Hook to monitor backend health status with retries
+ */
+export function useBackendHealth(pollingInterval = 5000) {
+  const [health, setHealth] = useState<BackendHealthState>({
+    status: tauriBackendService.isBackendRunning() ? 'healthy' : 'stopped',
+    isChecking: false,
+    error: null,
+  });
+
+  const checkHealth = useCallback(async () => {
+    setHealth((current) => ({
+      ...current,
+      status: current.status === 'healthy' ? 'healthy' : 'starting',
+      isChecking: true,
+      error: 'Backend starting up...',
+      lastChecked: Date.now(),
+    }));
+
+    try {
+      const isHealthy = await tauriBackendService.checkBackendHealth();
+
+      setHealth({
+        status: isHealthy ? 'healthy' : 'unhealthy',
+        lastChecked: Date.now(),
+        message: isHealthy ? 'Backend is healthy' : 'Backend is unavailable',
+        isChecking: false,
+        error: isHealthy ? null : 'Backend offline',
+      });
+
+      return isHealthy;
+    } catch (error) {
+      console.error('[BackendHealth] Health check failed:', error);
+      setHealth({
+        status: 'unhealthy',
+        lastChecked: Date.now(),
+        message: 'Backend is unavailable',
+        isChecking: false,
+        error: 'Backend offline',
+      });
+      return false;
+    }
+  }, []);
+
+  useEffect(() => {
+    let isMounted = true;
+
+    const initialize = async () => {
+      setHealth((current) => ({
+        ...current,
+        status: tauriBackendService.isBackendRunning() ? 'starting' : 'stopped',
+        isChecking: true,
+        error: 'Backend starting up...',
+      }));
+
+      await checkHealth();
+      if (!isMounted) return;
+    };
+
+    initialize();
+
+    const interval = setInterval(() => {
+      if (!isMounted) return;
+      void checkHealth();
+    }, pollingInterval);
+
+    return () => {
+      isMounted = false;
+      clearInterval(interval);
+    };
+  }, [checkHealth, pollingInterval]);
+
+  return {
+    ...health,
+    isHealthy: health.status === 'healthy',
+    checkHealth,
+  };
+}