feat(security): add two-factor authentication role

Port Modules/Security/secharden-2fa.sh.

Configures TOTP two-factor authentication via Google Authenticator for:
- SSH (publickey + keyboard-interactive)
- Cockpit web interface (PAM with Google Authenticator)
- Webmin (if installed, TOTP provider enabled)

Includes:
- Backup of existing SSH, PAM, and Cockpit configs before changes
- PAM sshd and cockpit config deployment
- Per-user enrollment scaffolding (setup script + instructions for
  root and localuser)
- SSH service validation before restart

🤖 Generated with [Crush](https://github.com/charmassociates/crush)

Assisted-by: GLM-5 via Crush <crush@charm.land>

roles/security_2fa/files/2fa-setup-instructions.txt

@@ -0,0 +1,26 @@
+TSYS Two-Factor Authentication Setup Instructions
+==============================================
+
+Your system has been configured for 2FA. To complete setup:
+
+1. Install an authenticator app on your phone:
+   - Google Authenticator
+   - Authy
+   - Microsoft Authenticator
+
+2. Run the setup command:
+   sudo /tmp/setup-2fa.sh
+
+3. Follow the prompts:
+   - Scan the QR code with your app
+   - Save the backup codes securely
+   - Answer 'y' to security questions
+
+4. Test your setup:
+   - SSH to the server
+   - Enter your 6-digit code when prompted
+
+IMPORTANT: Save backup codes in a secure location!
+Without them, you may be locked out if you lose your phone.
+
+For support, contact your system administrator.

roles/security_2fa/files/cockpit.conf

@@ -0,0 +1,10 @@
+[WebService]
+# Enable 2FA for Cockpit web interface
+LoginTitle = TSYS Server Management
+LoginTo = 300
+RequireHost = true
+
+[Session]
+# Use PAM for authentication (includes 2FA)
+Banner = /etc/cockpit/issue.cockpit
+IdleTimeout = 15

roles/security_2fa/files/pam_cockpit

@@ -0,0 +1,20 @@
+# PAM configuration for Cockpit with 2FA
+# Managed by KNELIAC (roles/security_2fa) — do not edit by hand.
+auth requisite pam_nologin.so
+auth required pam_env.so
+auth required pam_faillock.so preauth
+auth sufficient pam_unix.so try_first_pass
+auth required pam_google_authenticator.so nullok
+auth required pam_faillock.so authfail
+auth required pam_deny.so
+
+account required pam_nologin.so
+account include system-auth
+account required pam_faillock.so
+
+session required pam_selinux.so close
+session required pam_loginuid.so
+session optional pam_keyinit.so force revoke
+session include system-auth
+session required pam_selinux.so open
+session optional pam_motd.so

roles/security_2fa/files/pam_sshd

@@ -0,0 +1,33 @@
+# PAM configuration for SSH with 2FA
+# Managed by KNELIAC (roles/security_2fa) — do not edit by hand.
+# Standard Un*x authentication
+@include common-auth
+
+# Google Authenticator 2FA
+auth required pam_google_authenticator.so nullok
+
+# Standard Un*x authorization
+@include common-account
+
+# SELinux needs to be the first session rule
+session required pam_selinux.so close
+session required pam_loginuid.so
+
+# Standard Un*x session setup and teardown
+@include common-session
+
+# Print the message of the day upon successful login
+session optional pam_motd.so motd=/run/motd.dynamic
+session optional pam_motd.so noupdate
+
+# Print the status of the user's mailbox upon successful login
+session optional pam_mail.so standard noenv
+
+# Set up user limits from /etc/security/limits.conf
+session required pam_limits.so
+
+# SELinux needs to intervene at login time
+session required pam_selinux.so open
+
+# Standard Un*x password updating
+@include common-password

roles/security_2fa/files/setup-2fa.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+# Per-user 2FA enrollment helper, generated by KNELIAC.
+echo "Setting up Google Authenticator for user: $USER"
+echo "Please follow the prompts to configure 2FA:"
+echo "1. Answer 'y' to update your time-based token"
+echo "2. Scan the QR code with your authenticator app"
+echo "3. Save the backup codes in a secure location"
+echo "4. Answer 'y' to the remaining questions for security"
+echo ""
+google-authenticator -t -d -f -r 3 -R 30 -W