Introduce a new production desktop shell at `shells/desktop/shell` built with C++20, Qt Quick/QML, and LayerShellQt, including top bar, launcher, desktop surfaces, shell state, and mock app data. Add the shared `packages/nebula-ui` QML module (theme, controls, focus, icons) and wire it into the shell build.
Retire the old GTK/WebKit native host by removing `shells/desktop/native`, move the React shell UI to `shells/desktop/prototype-react` as an archived design reference, and update root/compositor/session documentation to reflect the new Linux-only production architecture and temporary Sway role.
Introduce a Linux-only C++20 `nebula-shell` host built with CMake, GTK4, gtk4-layer-shell, and WebKitGTK 6.0. Add a shared `Surface` abstraction and concrete Desktop/TopBar/Launcher surfaces with layer placement, sizing, transparency, and per-surface `?surface=` URL loading.
Add `ShellApplication` startup flow that validates `NEBULA_SHELL_DEV_URL`, checks layer-shell support, creates/presents desktop and top bar, and keeps launcher created but hidden for future bridge-driven toggling. Update the native README to document architecture, development setup, dependencies, and current milestone scope.
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.
andrew