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.

shells/desktop/ui/src/App.jsx

@@ -0,0 +1,18 @@
+import { getSurfaceName, SURFACES } from './lib/surface.js';
+import { DesktopSurface } from './surfaces/DesktopSurface.jsx';
+import { LauncherSurface } from './surfaces/LauncherSurface.jsx';
+import { PreviewSurface } from './surfaces/PreviewSurface.jsx';
+import { TopBarSurface } from './surfaces/TopBarSurface.jsx';
+
+const SURFACE_VIEWS = {
+  [SURFACES.DESKTOP]: DesktopSurface,
+  [SURFACES.TOPBAR]: TopBarSurface,
+  [SURFACES.LAUNCHER]: LauncherSurface,
+  [SURFACES.PREVIEW]: PreviewSurface,
+};
+
+export default function App() {
+  const surface = getSurfaceName();
+  const View = SURFACE_VIEWS[surface] ?? PreviewSurface;
+  return <View />;
+}