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/programs.nix

@@ -0,0 +1,41 @@
+{ ... }:
+{
+  flake.modules.nixos.common-programs = { lib, pkgs, ... }: {
+    environment = {
+      systemPackages = with pkgs; [
+        ### Dev Tools ###
+        git
+        ### System Utilities ###
+        btop
+        fastfetch
+        helix
+        nixos-firewall-tool
+        nvd
+        sysz
+        tmux
+        wget
+        yazi
+      ];
+      shellAliases = {
+        cat = "${lib.getExe pkgs.bat} --paging=never --style=plain";
+        ls = "${lib.getExe pkgs.eza} --icons --group-directories-first";
+        tree = "ls --tree";
+      };
+    };
+
+    programs = {
+      command-not-found.enable = false;
+      fish = {
+        enable = true;
+        interactiveShellInit = ''
+          set fish_greeting
+          if set -q SSH_CONNECTION
+            export TERM=xterm-256color
+            clear
+            fastfetch
+          end
+        '';
+      };
+    };
+  };
+}