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 <connor@stirlingpdf.com>
Co-authored-by: James Brunton <james@stirlingpdf.com>
Co-authored-by: James Brunton <jbrunton96@gmail.com>

DeveloperGuide.md

@@ -32,6 +32,12 @@ This guide focuses on developing for Stirling 2.0, including both the React fron
 - Docker for containerization
 - Gradle for build management
 
+**Desktop Application (Tauri):**
+- Tauri for cross-platform desktop app packaging
+- Rust backend for system integration
+- PDF file association support
+- Self-contained JRE bundling with JLink
+
 **Legacy (reference only during development):**
 - Thymeleaf templates (being completely replaced in 2.0)
 
@@ -44,6 +50,8 @@ This guide focuses on developing for Stirling 2.0, including both the React fron
 - Java JDK 17 or later (JDK 21 recommended)
 - Node.js 18+ and npm (required for frontend development)
 - Gradle 7.0 or later (Included within the repo)
+- Rust and Cargo (required for Tauri desktop app development)
+- Tauri CLI (install with `cargo install tauri-cli`)
 
 ### Setup Steps
 
@@ -95,6 +103,10 @@ Stirling 2.0 uses client-side file storage:
 ### Legacy Code Reference
 The existing Thymeleaf templates remain in the codebase during development as reference material but will be completely removed for the 2.0 release.
 
+### Tauri Desktop App Development
+Stirling-PDF can be packaged as a cross-platform desktop application using Tauri with PDF file association support and bundled JRE.
+See [the frontend README](frontend/README.md#tauri) for build instructions.
+
 ## 5. Project Structure
 
 ```bash
@@ -109,6 +121,12 @@ Stirling-PDF/
 │   │   ├── services/      # API and utility services
 │   │   ├── types/         # TypeScript type definitions
 │   │   └── utils/         # Utility functions
+│   ├── src-tauri/         # Tauri desktop app configuration
+│   │   ├── src/           # Rust backend code
+│   │   ├── libs/          # JAR files (generated by build scripts)
+│   │   ├── runtime/       # Bundled JRE (generated by build scripts)
+│   │   ├── Cargo.toml     # Rust dependencies
+│   │   └── tauri.conf.json # Tauri configuration
 │   ├── public/
 │   │   └── locales/       # Internationalization files (JSON)
 │   ├── package.json       # Frontend dependencies
@@ -392,23 +410,23 @@ For Stirling 2.0, new features are built as React components instead of Thymelea
    // frontend/src/tools/NewTool.tsx
    import { useState } from 'react';
    import { Button, FileInput, Container } from '@mantine/core';
-   
+
    interface NewToolProps {
      params: Record<string, any>;
      updateParams: (updates: Record<string, any>) => void;
    }
-   
+
    export default function NewTool({ params, updateParams }: NewToolProps) {
      const [files, setFiles] = useState<File[]>([]);
-     
+
      const handleProcess = async () => {
        // Process files using API or client-side logic
      };
-     
+
      return (
        <Container>
-         <FileInput 
-           multiple 
+         <FileInput
+           multiple
            accept="application/pdf"
            onChange={setFiles}
          />