FIX: Simplify sed command in add_disable_wpcron_to_config

Problem: Complex quoting in sed command caused 'extra characters after command' error
Solution: Use @ delimiter instead of # and simplify variable substitution

The issue was multi-level quote escaping that didn't work correctly.
Changed to simpler sed syntax with @ delimiter which handles special chars better.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

modules/website/wordpress/wordpress-cron-manager.sh

@@ -1585,16 +1585,16 @@ remove_disable_wpcron_from_config() {
 # Returns 0 on success, 1 on failure
 add_disable_wpcron_to_config() {
     local wp_config="$1"
+    local new_define="define('$WP_CRON_DISABLED_VAR', true);"
 
     # Try to insert before WordPress stop editing comment (proper convention)
     if grep -q "$WP_CONFIG_MARKER" "$wp_config" 2>/dev/null; then
-        sed -i '#'"$WP_CONFIG_MARKER"'#i\
-define('"'"''"$WP_CRON_DISABLED_VAR"''"'"', true);' "$wp_config"
+        # Use sed with @ delimiter to avoid escaping issues, insert before marker
+        sed -i.wpbak "@$WP_CONFIG_MARKER@i\\$new_define" "$wp_config"
         return 0
     elif grep -q "$WP_EDIT_START" "$wp_config"; then
         # Fallback: if no stop editing found, add after opening PHP tag
-        sed -i '#'"$WP_EDIT_START"'#a\
-define('"'"''"$WP_CRON_DISABLED_VAR"''"'"', true);' "$wp_config"
+        sed -i.wpbak "@$WP_EDIT_START@a\\$new_define" "$wp_config"
         return 0
     else
         # File format is unexpected