feat: add wireguard secure installer with modular architecture

This commit introduces a new WireGuard VPN installer with enterprise-grade security features. The installer includes:

- Zero-touch installation with automatic configuration
- Modular architecture for maintainability (separate lib files)
- Client management interface with bandwidth monitoring
- Support for multiple Linux distributions
- Secure defaults and hardened configurations

The implementation provides a complete solution for deploying WireGuard VPN servers with minimal user interaction while maintaining security best practices.

lib/os_detect.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+# WireGuard Secure Installer
+# Copyright (c) 2025 Muhammad Fadhila Abiyyu Faris
+# GitHub: [github.com/fadhila36/wireguard-secure-installer](https://github.com/fadhila36/wireguard-secure-installer)
+
+check_os() {
+    if [ -f /etc/os-release ]; then
+        . /etc/os-release
+        OS=$ID
+        VERSION_ID=$VERSION_ID
+    else
+        fatal_error "Cannot detect OS. /etc/os-release not found."
+    fi
+
+    log_info "Detected OS: $OS $VERSION_ID"
+
+    case "$OS" in
+        ubuntu|debian)
+            PKG_MANAGER="apt-get"
+            UPDATE_CMD="apt-get update"
+            INSTALL_CMD="apt-get install -y"
+            ;;
+        centos|rhel|rocky|almalinux)
+            PKG_MANAGER="dnf"
+            UPDATE_CMD="dnf check-update" # dnf update is slow, check-update is enough to refresh metadata
+            INSTALL_CMD="dnf install -y"
+            ;;
+        *)
+            fatal_error "Unsupported OS: $OS. Supported: Ubuntu, Debian, CentOS, Rocky, AlmaLinux."
+            ;;
+    esac
+}
+
+install_dependencies() {
+    log_info "Installing dependencies..."
+    
+    $UPDATE_CMD >> "$LOG_FILE" 2>&1
+
+    case "$OS" in
+        ubuntu|debian)
+            $INSTALL_CMD wireguard qrencode curl iptables >> "$LOG_FILE" 2>&1
+            ;;
+        centos|rhel|rocky|almalinux)
+            $INSTALL_CMD epel-release >> "$LOG_FILE" 2>&1
+            $INSTALL_CMD wireguard-tools qrencode curl iptables-services >> "$LOG_FILE" 2>&1
+            ;;
+    esac
+
+    if ! command -v wg >/dev/null; then
+        fatal_error "WireGuard installation failed."
+    fi
+}