Add comprehensive Plesk control panel support

Core Infrastructure Added:
- lib/plesk-helpers.sh: 30+ Plesk-specific helper functions
  - Domain discovery (list, docroot, logdir, access/error logs)
  - User/subscription management
  - Database discovery
  - PHP version detection (/opt/plesk/php/)
  - PHP-FPM pool discovery
  - Configuration file locations
  - Mail functions
  - Service management
  - Version detection with log structure handling

- lib/domain-discovery.sh: Unified control panel abstraction
  - Consistent API across cPanel, Plesk, InterWorx, standalone
  - list_all_domains() - works on any panel
  - get_domain_docroot() - panel-agnostic document root
  - get_domain_logdir() - panel-agnostic log discovery
  - get_domain_access_log() - access log paths
  - get_domain_error_log() - error log paths
  - get_all_log_files() - all logs across all domains
  - get_domain_owner() - domain owner/user
  - list_all_users() - user enumeration
  - get_domain_fpm_socket() - PHP-FPM pool sockets
  - get_domain_databases() - database discovery
  - domain_exists() - existence checks

Documentation:
- PLESK_REFERENCE.md: Complete Plesk architecture reference
  - Directory structure mapping
  - Log file locations (current & future versions)
  - PHP-FPM pool locations
  - Configuration file paths
  - Plesk CLI command reference
  - Key differences from cPanel
  - Subdomain handling differences

- PLESK_SUPPORT_SUMMARY.md: Implementation summary
  - All functions documented
  - Usage examples
  - Migration guide for existing modules
  - Version compatibility notes
  - Testing checklist

System Detection Enhanced:
- lib/system-detect.sh:
  - Improved Plesk detection with version-aware log paths
  - Auto-sources plesk-helpers.sh when Plesk detected
  - Added /opt/plesk/php/ scanning for PHP versions
  - Sets SYS_USER_HOME_BASE=/var/www/vhosts for Plesk

Email Menu Added:
- launcher.sh: New Email Troubleshooting menu category
  - 9 email diagnostic/maintenance tools (placeholders)
  - Deliverability test, queue inspector, SMTP test
  - SPF/DKIM/DMARC check, blacklist check
  - Mail log analyzer, queue flush
  - Mailbox cleanup, size reports

Plesk Architecture Support:
- /var/www/vhosts/ base directory structure
- system/DOMAIN/logs/ for Plesk <18.0.50
- DOMAIN/logs/ for Plesk 18.0.50+
- Automatic version detection
- Subdomain separate directory handling
- /opt/plesk/php/X.Y/ PHP version detection
- /var/www/vhosts/system/DOMAIN/php-fpm.sock pools
- /var/www/vhosts/system/DOMAIN/conf/ configs

Fallback Mechanisms:
- All functions work with or without Plesk CLI
- Directory scanning fallbacks
- MySQL direct query fallbacks
- Path inference from standard locations

Status: Core infrastructure complete, ready for module integration
Next: Test on actual Plesk server, update existing modules

Ref: system_map.tsv analysis from Plesk production system

lib/system-detect.sh

@@ -57,9 +57,21 @@ detect_control_panel() {
     if [ -f "/usr/local/psa/version" ]; then
         SYS_CONTROL_PANEL="plesk"
         SYS_CONTROL_PANEL_VERSION=$(cat /usr/local/psa/version | head -1)
-        SYS_LOG_DIR="/var/www/vhosts/system"
+
+        # Plesk uses /var/www/vhosts as base
         SYS_USER_HOME_BASE="/var/www/vhosts"
 
+        # Log directory depends on Plesk version
+        # Plesk 18.0.50+ uses /var/www/vhosts/DOMAIN/logs
+        # Plesk <18.0.50 uses /var/www/vhosts/system/DOMAIN/logs
+        # Set marker path - tools will use plesk_get_logdir() for actual path
+        SYS_LOG_DIR="/var/www/vhosts/system"
+
+        # Source Plesk helpers for advanced functionality
+        if [ -f "$LIB_DIR/plesk-helpers.sh" ]; then
+            source "$LIB_DIR/plesk-helpers.sh"
+        fi
+
         print_success "Detected Plesk v${SYS_CONTROL_PANEL_VERSION}"
         return 0
     fi
@@ -238,6 +250,16 @@ detect_php_versions() {
         done
     fi
 
+    # Check Plesk PHP versions (/opt/plesk/php/)
+    if [ "$SYS_CONTROL_PANEL" = "plesk" ]; then
+        for php_path in /opt/plesk/php/*/bin/php; do
+            if [ -x "$php_path" ]; then
+                local full_version=$($php_path -v 2>/dev/null | grep -oP '^PHP \K[\d.]+' | head -1)
+                [ -n "$full_version" ] && SYS_PHP_VERSIONS+=("$full_version")
+            fi
+        done
+    fi
+
     # Check alt-php versions (CloudLinux) - fast path parsing
     for php_path in /opt/alt/php*/usr/bin/php; do
         if [ -x "$php_path" ]; then
@@ -250,8 +272,8 @@ detect_php_versions() {
         fi
     done
 
-    # Remove duplicates
-    SYS_PHP_VERSIONS=($(echo "${SYS_PHP_VERSIONS[@]}" | tr ' ' '\n' | sort -u))
+    # Remove duplicates and sort by version
+    SYS_PHP_VERSIONS=($(echo "${SYS_PHP_VERSIONS[@]}" | tr ' ' '\n' | sort -u -V))
 
     if [ ${#SYS_PHP_VERSIONS[@]} -gt 0 ]; then
         print_success "Detected PHP versions: ${SYS_PHP_VERSIONS[*]}"