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/banner

@@ -0,0 +1,14 @@
+# SSH Login Banner
+# Deploy to: /etc/ssh/banner
+
+================================================================================
+                              AUTHORIZED ACCESS ONLY
+================================================================================
+
+This system is for authorized users only. All activity may be monitored and
+recorded. Unauthorized access is prohibited and will be prosecuted to the
+full extent of the law.
+
+If you are not an authorized user, disconnect immediately.
+
+================================================================================