Bootstrap NebulaOS repo and desktop shell UI

Initialize the NebulaOS monorepo layout with top-level documentation, ignore rules, placeholder service/package directories, compositor docs plus a baseline Sway config, and session startup/desktop entry files. Add the first desktop shell prototype under `shells/desktop/ui` using React + Vite, including themed surface components (desktop, top bar, launcher, preview), mock Nebula APIs and shell bridge state wiring, reusable UI controls/icons, and supporting styles/config needed for local development.

.gitignore

@@ -0,0 +1,31 @@
+# Node
+node_modules/
+dist/
+.vite/
+dist-ssr/
+*.local
+
+# CMake
+build/
+cmake-build-*/
+
+# Compiled objects
+*.o
+*.so
+*.a
+
+# IDE
+.idea/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+logs/
+
+# Environment
+.env
+.env.*
+!.env.example