fix(scripts): standardize source paths and quoting

- install-composer.sh: use $DOTFILES instead of $HOME/.dotfiles
- install-macos-defaults.sh: use $DOTFILES, replace which with command -v
- install-xcode-cli-tools.sh: quote command substitution
- create-nvim-keymaps.sh: quote $DEST in nvim redir command

scripts/install-macos-defaults.sh

@@ -8,7 +8,7 @@ set -uo pipefail
 [ "$(uname)" != "Darwin" ] && echo "Not a macOS system" && exit 0
 
 # shellcheck source=shared.sh
-source "$HOME/.dotfiles/config/shared.sh"
+source "$DOTFILES/config/shared.sh"
 
 msgr run "Starting to set macOS defaults, these require sudo privileges:"
 
@@ -24,12 +24,12 @@ while true; do
 done 2> /dev/null &
 
 # Skip when shell is fish
-if [[ $SHELL != $(which fish) ]]; then
+if [[ $SHELL != "$(command -v fish)" ]]; then
   msgr nested "Change user shell to zsh if it is available and not the current"
 
   # Change user shell to zsh if not that already.
   if hash zsh 2> /dev/null; then
-    [[ $SHELL != $(which zsh) ]] && chsh -s "$(which zsh)"
+    [[ $SHELL != "$(command -v zsh)" ]] && chsh -s "$(command -v zsh)"
   fi
 fi