refactor: implement component-based architecture for enhanced maintainability

- Reorganize directory structure into core/, features/, and themes/
- Colocate application Nix logic, configs, scripts, and theme overrides
- Implement 'Inversion of Control' for theming: apps now pull theme-specific layouts
- Update flake.nix and shared library paths to match the new structure
- Document the new Feature-Centric architecture in README.md

features/desktop/hyprland/config/xdph.conf

@@ -0,0 +1,4 @@
+screencopy {
+    allow_token_by_default = true
+    custom_picker_binary = hyprland-preview-share-picker
+}