fix: use zsh idioms and quote variables in shell config

- Use [[ ]] instead of [ ] for conditionals (zsh idiom)
- Quote variable expansions in ZINIT_HOME checks and dirname call
- Quote dollar-1 in mkcd function
- Remove extra blank line in .vimrc

Nightshift-Task: lint-fix
Nightshift-Ref: https://github.com/marcus/nightshift

.vimrc

@@ -24,7 +24,6 @@ set backupdir=~/.vim/backup//
 set nobackup
 set mouse=a             " mouse support
 
-
 noremap <Up> <NOP>
 noremap <Down> <NOP>
 noremap <Left> <NOP>

.zshrc

@@ -36,8 +36,8 @@ zmodload zsh/stat
 
 # plugin manager
 ZINIT_HOME="${XDG_DATA_HOME:-${HOME}}/.zinit.git"
-[ ! -d $ZINIT_HOME ] && mkdir -p "$(dirname $ZINIT_HOME)"
-[ ! -d $ZINIT_HOME/.git ] && git clone https://github.com/zdharma-continuum/zinit.git "$ZINIT_HOME"
+[[ ! -d "$ZINIT_HOME" ]] && mkdir -p "$(dirname "$ZINIT_HOME")"
+[[ ! -d "$ZINIT_HOME/.git" ]] && git clone https://github.com/zdharma-continuum/zinit.git "$ZINIT_HOME"
 source "${ZINIT_HOME}/zinit.zsh"
 
 zinit light zsh-users/zsh-autosuggestions
@@ -158,7 +158,7 @@ function y() {
   local tmp="$(mktemp -t "yazi-cwd.XXXXXX")" cwd
   command yazi "$@" --cwd-file="$tmp"
   IFS= read -r -d '' cwd < "$tmp"
-  [ "$cwd" != "$PWD" ] && [ -d "$cwd" ] && builtin cd -- "$cwd"
+  [[ "$cwd" != "$PWD" ]] && [[ -d "$cwd" ]] && builtin cd -- "$cwd"
   rm -f -- "$tmp"
 }
 
@@ -179,7 +179,7 @@ function clip {
 function mkcd {
   : "${1:?where?}"
   [[ -e $1 ]] && { echo "file exists"; return 1 }
-  mkdir -p $1 && cd $1
+  mkdir -p "$1" && cd "$1"
 }
 
 function cdtmp {