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

themes/palettes/retro-82/apps/neovim.lua

@@ -0,0 +1,13 @@
+return {
+  {
+    "OldJobobo/retro-82.nvim",
+    name = "retro-82",
+    priority = 1000,
+  },
+  {
+    "LazyVim/LazyVim",
+    opts = {
+      colorscheme = "retro-82",
+    },
+  },
+}