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

core/home/config/wiremix/wiremix.toml

@@ -0,0 +1,5 @@
+# overwrites default wiremix configuration
+# defaults: https://github.com/tsowell/wiremix/blob/main/wiremix.toml
+
+[char_sets.default]
+default_device = "⮞"