Add preview of changes before applying optimizations to Option 5

- Display all changes that will be made with per-domain breakdown
- Show memory impact per domain and total impact
- Calculate memory freed/allocated for each change
- Require final confirmation before actually applying changes
- Provides safety check to prevent accidental bad configurations

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

modules/performance/php-optimizer.sh

@@ -926,6 +926,110 @@ optimize_all_domains() {
             ;;
     esac
 
+    # ========================================================================
+    # STEP 3: PREVIEW CHANGES BEFORE APPLYING
+    # ========================================================================
+
+    show_banner
+    cecho "${WHITE}${BOLD}PREVIEW: Changes that will be applied${NC}"
+    cecho "${CYAN}─────────────────────────────────────────────────────────────────────${NC}"
+    echo ""
+
+    local preview_count=0
+    local preview_total_impact=0
+
+    # Get all users for preview
+    local preview_users
+    preview_users=$(list_all_users)
+
+    while IFS= read -r username; do
+        [ -z "$username" ] && continue
+
+        local user_domains
+        user_domains=$(get_user_domains "$username")
+
+        while IFS= read -r domain; do
+            [ -z "$domain" ] && continue
+
+            # Check if this domain/user was selected
+            local should_preview=false
+            if [ "$SYS_CONTROL_PANEL" = "cpanel" ]; then
+                [ "${domains_to_apply[$domain]}" = "true" ] && should_preview=true
+            else
+                [ "${domains_to_apply[$username]}" = "true" ] && should_preview=true
+            fi
+
+            if [ "$should_preview" = "false" ]; then
+                continue
+            fi
+
+            preview_count=$((preview_count + 1))
+
+            # Get current pool config
+            local pool_config
+            pool_config=$(find_fpm_pool_config "$username" "$domain" 2>/dev/null)
+
+            if [ -z "$pool_config" ] || [ ! -f "$pool_config" ]; then
+                continue
+            fi
+
+            # Get current and recommended values
+            local current_max recommended_max
+            current_max=$(grep "^pm.max_children" "$pool_config" 2>/dev/null | awk -F'=' '{print $2}' | tr -d ' ')
+
+            if [ "$SYS_CONTROL_PANEL" = "cpanel" ]; then
+                recommended_max="${recommended_values[$domain]}"
+            else
+                recommended_max="${recommended_values[$username]}"
+            fi
+
+            if [ -z "$current_max" ] || [ -z "$recommended_max" ]; then
+                continue
+            fi
+
+            # Calculate memory impact (assume 20MB per process on average)
+            local memory_freed=$((( current_max - recommended_max ) * 20))
+
+            if [ "$current_max" -ne "$recommended_max" ]; then
+                cecho "  ${CYAN}[$preview_count]${NC} $domain"
+                cecho "      Current: pm.max_children = ${YELLOW}$current_max${NC}"
+                cecho "      Change to: pm.max_children = ${GREEN}$recommended_max${NC}"
+
+                if [ "$memory_freed" -gt 0 ]; then
+                    cecho "      Memory freed: ${GREEN}+${memory_freed}MB${NC}"
+                    preview_total_impact=$((preview_total_impact + memory_freed))
+                elif [ "$memory_freed" -lt 0 ]; then
+                    cecho "      Memory allocated: ${YELLOW}$((-memory_freed))MB${NC} (growth)"
+                fi
+                echo ""
+            fi
+        done <<< "$user_domains"
+    done <<< "$preview_users"
+
+    if [ "$preview_count" -eq 0 ]; then
+        cecho "${YELLOW}No changes to preview${NC}"
+        echo ""
+        read -p "Press Enter to continue..."
+        return
+    fi
+
+    echo ""
+    cecho "${CYAN}═══════════════════════════════════════════════════════════════════${NC}"
+    cecho "${WHITE}${BOLD}PREVIEW SUMMARY${NC}"
+    cecho "  Total changes: ${WHITE}$preview_count${NC}"
+    if [ "$preview_total_impact" -gt 0 ]; then
+        cecho "  Total memory that could be freed: ${GREEN}+${preview_total_impact}MB${NC}"
+    fi
+    echo ""
+    cecho "${CYAN}─────────────────────────────────────────────────────────────────────${NC}"
+
+    # Ask for final confirmation before applying
+    if ! confirm "Apply these changes?"; then
+        cecho "${YELLOW}Optimization cancelled${NC}"
+        read -p "Press Enter to continue..."
+        return
+    fi
+
     show_banner
     cecho "${WHITE}${BOLD}Applying optimizations...${NC}"
     cecho "${CYAN}Selected: ${#domains_to_apply[@]} domain(s)/user(s)${NC}"