add aspects/common/ NixOS modules

Migrates common NixOS configuration to dendritic aspect pattern:
boot, console, firewall, locale, nix, openssh, programs, security,
services, tailscale, users

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

aspects/common/security.nix

@@ -0,0 +1,14 @@
+{ ... }:
+{
+  flake.modules.nixos.common-security = { ... }: {
+    security = {
+      unprivilegedUsernsClone = true; # Needed for rootless podman
+      sudo = {
+        wheelNeedsPassword = false;
+        extraConfig = ''
+          Defaults lecture = never
+        '';
+      };
+    };
+  };
+}