[ZSH] Speed up shell startup

Move antidote update from every shell start to update_mac.sh: it dropped
the bundle cache each time, forcing a rebuild on the next start. Background
the locale write and skip the brew --repository fork.

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

update_mac.sh

@@ -66,6 +66,11 @@ function update_others {
     echo "-- ALACRITTY"
     "$SCRIPT_DIR/install_alacritty_mac.sh" || echo "Alacritty update failed." >&2
 
+    if [ -f "$HOME/.antidote/antidote.zsh" ]; then
+        echo "-- ANTIDOTE"
+        zsh "$HOME/.antidote/antidote.zsh" update
+    fi
+
     if [ -x "$(command -v claude)" ]; then
         echo "-- CLAUDE"
         claude --update