fix(zsh): defend the sourced zshrc against the /etc/zshrc defaults

/etc/zshrc renders promptInit and environment.shellAliases after
interactiveShellInit, so both overrode the shared zshrc: the prompt
became `prompt suse` and ls/ll/l fell back to coreutils. The plugin
sourcing in the zshrc points at the Arch path /usr/share/zsh/plugins
and silently found nothing.

Clear promptInit, drop the three aliases with null, and enable the
syntax-highlighting and autosuggestions modules.

modules/desktop.nix

@@ -129,6 +129,32 @@ in
     source ${moonarchSrc}/defaults/shell/zshrc
   '';
 
+  # /etc/zshrc places promptInit after interactiveShellInit, and its default
+  # ends in `prompt suse`, which assigns PS1 — the same parameter as PROMPT.
+  # Left at the default it overwrites the prompt the sourced zshrc just set.
+  # The zshrc owns the prompt, so nothing else has to run here.
+  programs.zsh.promptInit = "";
+
+  # The zshrc sources both plugins from /usr/share/zsh/plugins, the path the
+  # Arch packages use; the lookups are guarded and silently find nothing here.
+  # These modules source the same plugins from the store instead. The strategy
+  # is the one the zshrc sets on Arch.
+  programs.zsh.syntaxHighlighting.enable = true;
+  programs.zsh.autosuggestions = {
+    enable = true;
+    strategy = [ "history" "completion" ];
+  };
+
+  # environment.shellAliases carries ls, ll and l as defaults, and /etc/zshrc
+  # renders them after interactiveShellInit, so they shadow the eza aliases of
+  # the sourced zshrc. null drops an alias. Scoped to zsh: bash keeps the
+  # coreutils ls, which is the only thing it has.
+  programs.zsh.shellAliases = {
+    ls = null;
+    ll = null;
+    l = null;
+  };
+
   # --- File manager ---
   #
   # Counterpart to thunar, thunar-volman, thunar-archive-plugin, tumbler and