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)

lib/reference-db.sh

@@ -252,7 +252,7 @@ build_domains_section() {
     # Count total domains for progress
     local total_domains=0
     for user in "${users[@]}"; do
-        local userdata_dir="/var/cpanel/userdata/${user}"
+        local userdata_dir="${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}/${user}"
         if [ -d "$userdata_dir" ]; then
             total_domains=$((total_domains + $(find "$userdata_dir" -type f ! -name "*.cache" ! -name "*.yaml" ! -name "*.json" ! -name "main*" ! -name "cache" ! -name "*_SSL" 2>/dev/null | wc -l)))
         fi
@@ -262,7 +262,7 @@ build_domains_section() {
 
     # Get detailed domain information from cPanel userdata (if available)
     for user in "${users[@]}"; do
-        local userdata_dir="/var/cpanel/userdata/${user}"
+        local userdata_dir="${SYS_CPANEL_USERDATA_DIR:-/var/cpanel/userdata}/${user}"
 
         if [ -d "$userdata_dir" ]; then
             # Parse each domain configuration file in userdata