Add PostgreSQL and Percona Server detection

- Add PostgreSQL detection via psql command
  * Detects version from psql --version
  * Sets SYS_DB_TYPE="postgresql"

- Add Percona Server detection as MySQL variant
  * Checks for 'Percona' in mysql --version output
  * Sets SYS_DB_TYPE="percona"
  * Distinguishes from standard MySQL and MariaDB

Impact: Toolkit now supports three database types:
- MySQL (traditional)
- MariaDB (drop-in replacement)
- Percona Server (high-performance variant)
- PostgreSQL (RDBMS alternative)

Makes toolkit compatible with broader range of server configurations.

lib/system-detect.sh

@@ -203,6 +203,7 @@ detect_web_server() {
 detect_database() {
     [ -n "$SYS_DETECTION_COMPLETE" ] || print_info "Detecting database server..."
 
+    # Check for MySQL/MariaDB/Percona
     if command_exists mysql; then
         local version_output=$(mysql --version 2>/dev/null)
 
@@ -210,6 +211,10 @@ detect_database() {
             SYS_DB_TYPE="mariadb"
             SYS_DB_VERSION=$(echo "$version_output" | grep -oP '\d+\.\d+\.\d+' | head -1)
             print_success "Detected MariaDB ${SYS_DB_VERSION}"
+        elif echo "$version_output" | grep -qi "percona"; then
+            SYS_DB_TYPE="percona"
+            SYS_DB_VERSION=$(echo "$version_output" | grep -oP '\d+\.\d+\.\d+' | head -1)
+            print_success "Detected Percona Server ${SYS_DB_VERSION}"
         else
             SYS_DB_TYPE="mysql"
             SYS_DB_VERSION=$(echo "$version_output" | grep -oP '\d+\.\d+\.\d+' | head -1)
@@ -218,8 +223,17 @@ detect_database() {
         return 0
     fi
 
+    # Check for PostgreSQL
+    if command_exists psql; then
+        local version_output=$(psql --version 2>/dev/null)
+        SYS_DB_TYPE="postgresql"
+        SYS_DB_VERSION=$(echo "$version_output" | grep -oP '\d+\.\d+' | head -1)
+        print_success "Detected PostgreSQL ${SYS_DB_VERSION}"
+        return 0
+    fi
+
     SYS_DB_TYPE="none"
-    print_warning "No MySQL/MariaDB detected"
+    print_warning "No MySQL/MariaDB/PostgreSQL detected"
     return 1
 }