Add SSH hardening and kernel security configurations

- config/ssh/sshd_config_hardening: Enhanced SSH security settings
- config/ssh/banner: Legal warning banner for SSH connections
- config/sysctl/99-security.conf: Kernel network and memory protection parameters
- Includes deployment instructions for system-level hardening

config/ssh/sshd_config_hardening

@@ -0,0 +1,22 @@
+# SSH Hardening Configuration
+# Deploy by appending to: /etc/ssh/sshd_config
+# 
+# Setup commands:
+#   sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.backup
+#   sudo cat config/ssh/sshd_config_hardening >> /etc/ssh/sshd_config
+#   sudo sshd -t
+#   sudo systemctl restart sshd
+
+# Enhanced security settings
+ClientAliveInterval 300
+ClientAliveCountMax 2
+Compression no
+LogLevel VERBOSE
+MaxSessions 3
+TCPKeepAlive no
+X11Forwarding no
+AllowAgentForwarding no
+AllowTcpForwarding no
+GatewayPorts no
+PermitTunnel no
+Banner /etc/ssh/banner