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/apps/walker.nix

@@ -0,0 +1,56 @@
+{ config, pkgs, lib, ... }:
+
+{
+  programs.walker = {
+    enable = lib.mkDefault true;
+    runAsService = lib.mkDefault true;
+    config = lib.mkDefault {
+      theme = "nomarchy";
+      ui = {
+        anchors = {
+          top = true;
+        };
+      };
+      selection_wrap = true;
+      hide_action_hints = true;
+      placeholders = {
+        "default" = { input = " Search..."; list = "No Results"; };
+      };
+      keybinds = {
+        quick_activate = [];
+      };
+      columns = {
+        symbols = 1;
+      };
+      providers = {
+        max_results = 256;
+        default = [
+          "desktopapplications"
+          "websearch"
+        ];
+        prefixes = [
+          { prefix = "/"; provider = "providerlist"; }
+          { prefix = "."; provider = "files"; }
+          { prefix = ":"; provider = "symbols"; }
+          { prefix = "="; provider = "calc"; }
+          { prefix = "@"; provider = "websearch"; }
+          { prefix = "$"; provider = "clipboard"; }
+        ];
+      };
+    };
+    themes."nomarchy" = lib.mkDefault {
+      style = ''
+        * {
+          color: #${config.colorScheme.palette.base05};
+        }
+        #window {
+          background-color: #${config.colorScheme.palette.base00};
+        }
+        .item.active {
+          background-color: #${config.colorScheme.palette.base03};
+          color: #${config.colorScheme.palette.base0B};
+        }
+      '';
+    };
+  };
+}