refactor: see details below

- Fix emailing.
- Updated manage.sh to enhance command handling and service management for backend and frontend.
- Introduced utility functions for better code organization and readability.
- Added support for checking Node.js version and ensuring the virtual environment is set up.
- Implemented improved logging with color-coded output for better visibility.
- Created a new nginx.conf.example file for easy Nginx configuration setup for the application.

checkin-app.service.example

@@ -0,0 +1,70 @@
+# ==============================================================================
+# CheckIn App V2 - Systemd Service File Example
+# ==============================================================================
+#
+# This file defines a systemd service for running the CheckIn App backend
+#
+# Installation:
+#   1. Copy this file: sudo cp checkin-app.service.example /etc/systemd/system/checkin-app.service
+#   2. Edit the file and replace placeholders with your actual values
+#   3. Reload systemd: sudo systemctl daemon-reload
+#   4. Enable service: sudo systemctl enable checkin-app.service
+#   5. Start service: sudo systemctl start checkin-app.service
+#   6. Check status: sudo systemctl status checkin-app.service
+#
+# Management Commands:
+#   Start:   sudo systemctl start checkin-app
+#   Stop:    sudo systemctl stop checkin-app
+#   Restart: sudo systemctl restart checkin-app
+#   Status:  sudo systemctl status checkin-app
+#   Logs:    sudo journalctl -u checkin-app -f
+#
+# ==============================================================================
+
+[Unit]
+Description=CheckIn App V2 - Backend API Service
+Documentation=https://github.com/Cccc-owo/CheckInApp
+After=network.target
+Wants=network-online.target
+
+[Service]
+Type=forking
+
+# CHANGE THIS: Replace with your actual installation path
+# Example: /home/username/CheckInApp
+WorkingDirectory=/path/to/CheckInApp
+
+# PID file written by manage.sh
+PIDFile=/path/to/CheckInApp/backend.pid
+
+# Start backend using manage.sh script
+ExecStart=/path/to/CheckInApp/manage.sh start backend
+
+# Stop backend using manage.sh script
+ExecStop=/path/to/CheckInApp/manage.sh stop backend
+
+# Restart policy
+Restart=always
+RestartSec=10
+
+# Kill settings
+KillSignal=SIGTERM
+KillMode=mixed
+
+# Timeout settings
+TimeoutStartSec=60
+TimeoutStopSec=30
+
+# Resource limits
+LimitNOFILE=65535
+
+# Security settings
+NoNewPrivileges=true
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=checkin-app
+
+[Install]
+WantedBy=multi-user.target