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

src/user/modules/git/scripts/cdg.nix

@@ -1,24 +0,0 @@
-''
-function cdg() {
-  if [[ $1 == "--help" ]]; then
-    echo "A simple utility for navigating to the root of a git repo"
-    return 0
-  fi
-
-  if [[ -n "$1" ]]; then
-    echo "Invalid command: $1. Try 'cdg --help'."
-    return 1
-  fi
-
-  local root_dir
-  root_dir=$(git rev-parse --show-toplevel 2>/dev/null)
-  local git_status=$?
-
-  if [ $git_status -ne 0 ]; then
-    echo "Error: Not a git repo."
-    return 1
-  fi
-
-  cd "$root_dir"
-}
-''