zsh: use eza for ls/ll, add lt tree alias

exa is unmaintained and out of Debian entirely; eza is the maintained fork.
Guarded on eza being installed so machines without it keep the old ls
fallbacks, which are untouched.

zsh/aliases.zsh

@@ -29,7 +29,14 @@ alias cls='clear;ls'
 alias df='df -h'
 alias du='du -h -d 2'
 
-if [[ $platform == 'linux' ]]; then
+# eza if it is installed, plain ls otherwise. This file is shared across every machine
+# and not all of them have eza, so the fallbacks stay exactly as they were.
+# (eza is the maintained fork of exa; exa itself is unmaintained and out of Debian.)
+if (( $+commands[eza] )); then
+  alias ls='eza --group-directories-first'
+  alias ll='eza -lah --git --group-directories-first'
+  alias lt='eza --tree --level=2 --group-directories-first'
+elif [[ $platform == 'linux' ]]; then
   alias ll='ls -alh --color=auto'
   alias ls='ls --color=auto'
 elif [[ $platform == 'darwin' ]]; then