Fix 9 MEDIUM hardcoded /var/cpanel paths - ALL MEDIUM ISSUES RESOLVED!

FIXES:
Changed hardcoded /var/cpanel paths to use environment variables with fallbacks:

reference-db.sh:
- Line 255: /var/cpanel/userdata → ${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}
- Line 265: /var/cpanel/userdata → ${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}

php-detector.sh:
- Line 69: /var/cpanel/userdata → ${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}

user-manager.sh:
- Line 44-45: /var/cpanel/users → ${SYS_CPANEL_USERS_DIR:-/var/cpanel/users}
- Line 111: /var/cpanel/users → ${SYS_CPANEL_USERS_DIR:-/var/cpanel/users}

diagnostic-report.sh:
- Line 68: /var/cpanel/users → ${SYS_CPANEL_USERS_DIR:-/var/cpanel/users}

wordpress-cron-manager.sh:
- Line 229-230: /var/cpanel/userdata → ${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}

IMPACT:
- Paths now configurable via environment variables
- Maintains backward compatibility with default paths
- Better multi-panel support flexibility
- More testable code (can override paths in tests)

QA STATUS:
🎉 ALL MEDIUM ISSUES RESOLVED! 🎉
- CRITICAL: 0 ✓
- HIGH: 0 ✓
- MEDIUM: 0 ✓
- LOW: 11 (remaining)

tools/diagnostic-report.sh

@@ -65,7 +65,8 @@ echo ""
 
     echo "--- USER/DOMAIN FILES ---"
     echo "cPanel user files:"
-    echo "  /var/cpanel/users/: $(ls /var/cpanel/users/ 2>/dev/null | wc -l) files"
+    local cpanel_users_dir="${SYS_CPANEL_USERS_DIR:-/var/cpanel/users}"
+    echo "  $cpanel_users_dir: $(ls "$cpanel_users_dir" 2>/dev/null | wc -l) files"
     echo "  /etc/trueuserdomains: $([ -f /etc/trueuserdomains ] && wc -l < /etc/trueuserdomains || echo "NOT FOUND") lines"
     echo "  /etc/userdatadomains: $([ -f /etc/userdatadomains ] && wc -l < /etc/userdatadomains || echo "NOT FOUND") lines"
     echo ""