fix: use initContent instead of deprecated initExtra for ZSH configuration

Replace deprecated programs.zsh.initExtra with programs.zsh.initContent
to follow current Home Manager conventions.

Author: svnlto

common/programs/default.nix

@@ -44,7 +44,7 @@ in {
     # Common aliases - platform-specific aliases merged separately
     shellAliases = sharedZsh.aliases;
 
-    initExtra = ''
+    initContent = ''
       ${sharedZsh.tools}
       ${sharedZsh.historyOptions}
       ${sharedZsh.options}