Add Plesk MySQL authentication support to database discovery

Problem: Plesk MySQL requires password authentication
  User report: "ERROR 1045 (28000): Access denied for user 'root'@'localhost'"
  Result: 0 databases detected on Plesk servers

Root Cause:
  Plesk stores MySQL admin password in /etc/psa/.psa.shadow
  All MySQL queries were using passwordless 'mysql' command
  This works on cPanel (uses ~/.my.cnf) but fails on Plesk

Solution: build_databases_section() in lib/reference-db.sh
  1. Check if running on Plesk and /etc/psa/.psa.shadow exists
  2. Read admin password from file
  3. Build mysql_cmd variable with credentials
  4. Use $mysql_cmd for all database queries

Changes (lib/reference-db.sh):
  Lines 161-166: Added Plesk credential detection
  Line 168: Use $mysql_cmd for SHOW DATABASES
  Line 179: Use $mysql_cmd for size calculation
  Line 184: Use $mysql_cmd for table count

Impact:
  ✅ Database discovery now works on Plesk
  ✅ Backwards compatible with cPanel/InterWorx/Standalone
  ✅ No performance impact (password read once)

Status: Ready for testing on Plesk server

lib/reference-db.sh

@@ -158,7 +158,14 @@ build_databases_section() {
         return
     fi
 
-    local all_dbs=$(mysql -Ns -e "SHOW DATABASES" 2>/dev/null | grep -v "^information_schema$\|^mysql$\|^performance_schema$\|^sys$" || true)
+    # Build MySQL command with credentials if needed
+    local mysql_cmd="mysql"
+    if [ "$SYS_CONTROL_PANEL" = "plesk" ] && [ -f /etc/psa/.psa.shadow ]; then
+        local plesk_mysql_pass=$(cat /etc/psa/.psa.shadow)
+        mysql_cmd="mysql -uadmin -p${plesk_mysql_pass}"
+    fi
+
+    local all_dbs=$($mysql_cmd -Ns -e "SHOW DATABASES" 2>/dev/null | grep -v "^information_schema$\|^mysql$\|^performance_schema$\|^sys$" || true)
     local total_dbs=$(echo "$all_dbs" | wc -l)
     local current=0
 
@@ -169,12 +176,12 @@ build_databases_section() {
         local owner=$(get_database_owner "$db")
         local domain=$(get_database_domain "$db")
 
-        local size_mb=$(mysql -Ns -e "SELECT ROUND(SUM(data_length + index_length) / 1024 / 1024, 2)
+        local size_mb=$($mysql_cmd -Ns -e "SELECT ROUND(SUM(data_length + index_length) / 1024 / 1024, 2)
                                        FROM information_schema.TABLES
                                        WHERE table_schema='$db'" 2>/dev/null)
         [ -z "$size_mb" ] && size_mb=0
 
-        local table_count=$(mysql -Ns "$db" -e "SHOW TABLES" 2>/dev/null | wc -l)
+        local table_count=$($mysql_cmd -Ns "$db" -e "SHOW TABLES" 2>/dev/null | wc -l)
 
         echo "DB|$db|$owner|$domain|$size_mb|$table_count" >> "$SYSREF_DB"
     done