Fix menu standards: Replace plain dashes with Unicode separators

Replaced all plain dash separators (---) with Unicode (───) for consistency:

Fixed lib/common-functions.sh (1):
- print_section(): 79 dashes → 79 unicode dashes

Fixed lib/user-manager.sh (4):
- All occurrences: 79 dashes → 79 unicode dashes (replace_all)

Fixed modules/performance/php-optimizer.sh (1):
- Table separator: 104 dashes → 104 unicode dashes

Fixed modules/security/malware-scanner.sh (4):
- All occurrences: 40 dashes → 40 unicode dashes (replace_all)

All 8/8 separator issues resolved. Menus now have consistent Unicode styling.

modules/performance/php-optimizer.sh

@@ -1501,7 +1501,7 @@ check_server_memory_capacity() {
         local header
         header=$(echo "$recommendations" | head -1)
         echo "$header" | awk -F'|' '{printf "%-15s %8s %10s %12s %12s %15s %20s\n", $1, $2, $3, $4, $5, $6, $7}'
-        echo "--------------------------------------------------------------------------------------------------------"
+        echo "────────────────────────────────────────────────────────────────────────────────────────────────────────"
 
         # Display recommendations
         echo "$recommendations" | tail -n +2 | while IFS='|' read -r user current_max avg_mb traffic_rpm recommended_max allocated_mb reason; do