feat(upstream): switch to remote git repository for engine

- Update installer to use git+https://git.bemagri.xyz/bernardo/Nomarchy.git
- Remove redundant bundling/copying of the engine to /etc/nixos/nomarchy
- Expose all themes via xdg.dataFile for script accessibility
- Update theme scripts to resolve directories via local share instead of hardcoded system paths
- Update documentation to reflect the new remote-first architecture

GEMINI.md

@@ -25,7 +25,7 @@ The installer is designed to bootstrap a fresh system with this modular structur
 1.  **Repo Detection:** Identifies the location of the Nomarchy source.
 2.  **Scaffolding:** Creates a new downstream `flake.nix` that imports Nomarchy core modules.
 3.  **User Files:** Generates skeleton `system.nix` and `home.nix` files for the user to customize.
-4.  **Bundling:** Copies the entire Nomarchy source to `/etc/nixos/nomarchy` so the system can be rebuilt offline.
+4.  **Flake Updates:** Uses the public Git repository as the upstream source, allowing users to update their system via `nix flake update`.
 
 ### 3. Home Manager Integration
 * **Hybrid Declarative State:** While the distro is declarative, it uses state files in `~/.config/home-manager/` (managed by the distro's scripts) to allow for instant UI feedback (theming, fonts, wallpapers) without needing a full system rebuild for every small tweak.