refactor: reorganize flake structure and consolidate user config

Directory structure:
- Move from src/ to root level (system/, user/)
- Remove unused machines (workstation, vm, laptop)

User configuration:
- Add user/home.nix for shared defaults (pass, essentials, default modules)
- Centralize user options in user/default.nix
- Move submodules to consistent paths (bash/bash, git/git, neovim/nvim, vim/vim)

Module reorganization:
- Flatten nested module structures (remove /modules/ subdirs)
- Split CLI vs GUI tools (dev/ for CLI, gui/dev/ for GUI)
- Move neovim/vim to top-level modules (not under utils/)
- Remove security.enable - pass now in user/home.nix
- Remove utils.enable - essentials now in user/home.nix
- Add security/yubikey module with yubikey-manager, age-plugin-yubikey
- Move pcb, design to gui/dev/
- Replace penpot docker wrapper with nixpkgs penpot-desktop
- Remove i3 config
- Remove deprecated wsl.nativeSystemd option

GUI improvements:
- Browser-focused mimeApps in gui/default.nix
- Each WM handles its own auto-start via profileExtra

Cleanup:
- Update README with new structure
- Update justfile paths and valid systems
- Fix submodule paths in .gitmodules

user/modules/gui/corn/default.nix

@@ -0,0 +1,36 @@
+{ pkgs, lib, config, ... }:
+
+with lib;
+let
+  cfg = config.modules.user.gui.corn;
+
+in
+{ options.modules.user.gui.corn = { enable = mkEnableOption "Enable Bitcoin client applications"; };
+  config = mkIf cfg.enable {
+    home.packages = with pkgs; [
+      #trezor-suite
+      #trezorctl
+      #trezord
+
+      sparrow
+    ];
+
+    #systemd.user.services = {
+    #  trezord = {
+    #    Unit = {
+    #      Description = "Trezor Bridge";
+    #      After = [ "network.target" ];
+    #      Wants = [ "network.target" ];
+    #      PartOf = [ "graphical-session.target" ];
+    #    };
+    #    Service = {
+    #      ExecStart = "${pkgs.trezord}/bin/trezord-go";
+    #      Restart = "always";
+    #    };
+    #    Install = {
+    #      WantedBy = [ "default.target" ];
+    #    };
+    #  };
+    #};
+  };
+}