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/boot.nix

@@ -0,0 +1,21 @@
+{ ... }:
+{
+  flake.modules.nixos.common-boot = { pkgs, ... }: {
+    boot = {
+      loader = {
+        timeout = 1;
+        efi.canTouchEfiVariables = true;
+        systemd-boot = {
+          enable = true;
+          editor = false;
+          consoleMode = "max";
+          sortKey = "aa";
+          netbootxyz = {
+            enable = true;
+            sortKey = "zz";
+          };
+        };
+      };
+    };
+  };
+}