zsh: install .zshenv, back it up first, dedupe config URL

- Add configs/.zshenv (skip_global_compinit=1) and download it in zsh.sh
- Back up existing ~/.zshenv alongside ~/.zshrc before overwriting
- Factor the raw config URL into CONFIG_BASE_URL
- Source zsh-autocomplete before oh-my-zsh instead of via plugins=()

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

configs/.zshenv

@@ -0,0 +1 @@
+skip_global_compinit=1

configs/.zshrc

@@ -18,6 +18,8 @@ fi
 # Path to your oh-my-zsh installation.
   export ZSH=~/.oh-my-zsh
 
+source $ZSH/custom/plugins/zsh-autocomplete/zsh-autocomplete.plugin.zsh
+
 # Set the name of the theme to load. If you set this to "random"
 # It'll load a random theme each time that oh-my-zsh is loaded.
 # See https://github.com/robbyrussell/oh-my-zsh/wiki/Themes
@@ -79,11 +81,10 @@ plugins=(
 	git
 	zsh-history-substring-search
 	zsh-autosuggestions
- zsh-autocomplete
 #	zsh-eza
 	fzf-zsh-plugin
  	zsh-syntax-highlighting
-	
+
 )
 
 source $ZSH/oh-my-zsh.sh