Add Tauri app skeleton and project files

Initialize the Nebula OS Tauri project: add frontend (src/) with HTML, JS, CSS and SVG assets, plus a sample greet UI. Add src-tauri Rust backend (Cargo.toml, build.rs, main/lib) with a greeting command, tauri.conf.json, capability schema and platform icons. Add package.json (dev dependency on @tauri-apps/cli), .gitignore files and VSCode recommended extensions. Expand README with project vision, architecture and phase roadmap to document the Windows-first development plan.

src-tauri/src/main.rs

@@ -0,0 +1,6 @@
+// Prevents additional console window on Windows in release, DO NOT REMOVE!!
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+fn main() {
+    nebula_os_lib::run()
+}