FRE-606: Add Tauri desktop framework with cross-platform support

- Configure Tauri v2 for macOS, Windows, Linux
- Implement native menu bar (File, Edit, View, Window, Help)
- Add system tray with show/hide/quit functionality
- Create auto-updater framework with periodic checks
- Set up window state persistence
- Configure plugins (fs, http, dialog, shell, store)
- Add build scripts for all platforms
- Include comprehensive documentation

Files:
- src-tauri/Cargo.toml
- src-tauri/tauri.conf.json
- src-tauri/build.rs
- src-tauri/src/main.rs
- src-tauri/src/lib.rs
- src-tauri/src/menu.rs
- src-tauri/src/tray.rs
- src-tauri/src/updater.rs
- src-tauri/Cargo.lock
- src-tauri/icons/tray-icon.svg
- src-tauri/tauri.build.conf
- src-tauri/README.md
- .gitignore
- package.json (Tauri CLI scripts)

src-tauri/icons/tray-icon.svg

@@ -0,0 +1,6 @@
+<!-- Placeholder for tray icon -->
+<!-- This will be generated by the icon build process -->
+<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
+  <rect width="32" height="32" fill="#4A90D9" rx="6"/>
+  <text x="16" y="20" font-family="Arial" font-size="14" font-weight="bold" fill="white" text-anchor="middle">F</text>
+</svg>