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.

README.md

@@ -0,0 +1,20 @@
+# NebulaOS
+
+A Linux desktop environment built around a custom compositor, shell, and service stack.
+
+## Structure
+
+| Path | Purpose |
+|------|---------|
+| `core/nebula-core` | Core runtime and platform APIs |
+| `compositor/` | Compositor configuration (Sway) |
+| `shells/` | Desktop and bigscreen shell implementations |
+| `packages/` | Shared UI libraries, icons, API, and design tokens |
+| `services/` | System services (audio, network, bluetooth, power, accounts) |
+| `session/` | Session manager and desktop entry |
+| `packaging/` | Distribution packaging (Ubuntu) |
+| `branding/` | Boot assets, wallpapers, and sounds |
+
+## Getting started
+
+Documentation and build instructions will be added as components land.