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/components/BackendHealthIndicator.tsx

@@ -0,0 +1,80 @@
+import React, { useMemo, useCallback } from 'react';
+import { useTranslation } from 'react-i18next';
+import { Box, Tooltip, useMantineTheme, useComputedColorScheme, rem } from '@mantine/core';
+import { useBackendHealth } from '@app/hooks/useBackendHealth';
+
+interface BackendHealthIndicatorProps {
+  className?: string;
+}
+
+export const BackendHealthIndicator: React.FC<BackendHealthIndicatorProps> = ({
+  className = ''
+}) => {
+  const { t } = useTranslation();
+  const theme = useMantineTheme();
+  const colorScheme = useComputedColorScheme('light');
+  const { isHealthy, isChecking, checkHealth } = useBackendHealth();
+
+  const label = useMemo(() => {
+    if (isChecking) {
+      return t('backendHealth.checking', 'Checking backend status...');
+    }
+
+    if (isHealthy) {
+      return t('backendHealth.online', 'Backend Online');
+    }
+
+    return t('backendHealth.offline', 'Backend Offline');
+  }, [isChecking, isHealthy, t]);
+
+  const dotColor = useMemo(() => {
+    if (isChecking) {
+      return theme.colors.yellow?.[5] ?? '#fcc419';
+    }
+    if (isHealthy) {
+      return theme.colors.green?.[5] ?? '#37b24d';
+    }
+    return theme.colors.red?.[6] ?? '#e03131';
+  }, [isChecking, isHealthy, theme.colors.green, theme.colors.red, theme.colors.yellow]);
+
+  const handleKeyDown = useCallback((event: React.KeyboardEvent<HTMLSpanElement>) => {
+    if (event.key === 'Enter' || event.key === ' ') {
+      event.preventDefault();
+      checkHealth();
+    }
+  }, [checkHealth]);
+
+  return (
+    <Tooltip
+      label={label}
+      position="left"
+      offset={12}
+      withArrow
+      withinPortal
+      color={colorScheme === 'dark' ? undefined : 'dark'}
+    >
+      <Box
+        component="span"
+        className={className ? `${className}` : undefined}
+        role="status"
+        aria-live="polite"
+        aria-label={label}
+        tabIndex={0}
+        onClick={checkHealth}
+        onKeyDown={handleKeyDown}
+        style={{
+          width: rem(12),
+          height: rem(12),
+          borderRadius: '50%',
+          backgroundColor: dotColor,
+          boxShadow: colorScheme === 'dark'
+            ? '0 0 0 2px rgba(255, 255, 255, 0.18)'
+            : '0 0 0 2px rgba(0, 0, 0, 0.08)',
+          cursor: 'pointer',
+          display: 'inline-block',
+          outline: 'none',
+        }}
+      />
+    </Tooltip>
+  );
+};