fix: quote variables and use zsh idioms in shell config

- Quote ZINIT_HOME in plugin manager setup
- Quote $1 in mkcd function
- Use [[ ]] instead of [ ] in yazi wrapper (zsh idiom)
- Remove double 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

@@ -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 {