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/build.rs

@@ -0,0 +1,11 @@
+use tauri_build::Builder;
+
+fn main() {
+    Builder::default()
+        .plugin(tauri_plugin_fs::init())
+        .plugin(tauri_plugin_http::init())
+        .plugin(tauri_plugin_dialog::init())
+        .plugin(tauri_plugin_shell::init())
+        .plugin(tauri_plugin_store::init())
+        .build()
+}