Split shared host config into dedicated modules

- Add shared modules for boot, hardware, networking, input, and host defaults
- Move host-specific TOML flags to new option namespaces
- Update SSH and service defaults for the new layout

modules/nixos/shared/security/ssh.nix

@@ -4,7 +4,7 @@
     settings = {
       PasswordAuthentication = false;
       PermitEmptyPasswords = false;
-      PermitTunnel = false;
+      PermitTunnel = true;
       UseDns = false;
       KbdInteractiveAuthentication = false;
       X11Forwarding = config.services.xserver.enable;
@@ -14,7 +14,7 @@
       ClientAliveCountMax = 0;
       # AllowUsers = ["user"];
       TCPKeepAlive = false;
-      AllowTcpForwarding = false;
+      AllowTcpForwarding = "yes";
       AllowAgentForwarding = false;
       LogLevel = "VERBOSE";
       PermitRootLogin = "no";