feat: comprehensive NixOS and home-manager configuration updates

This commit includes significant updates to the Nix configuration including:
- Added common NixOS module with system packages
- Updated home-manager configurations for various systems
- Enhanced terminal programs including Claude Code integration
- Updated LLM server configurations with new models
- Improved btop configuration with custom package
- Added opencode support with permission settings
- Updated tmux and nvim configurations

The changes introduce new features, update existing configurations, and improve the overall system setup.

homes/aarch64-darwin/evanreichard@mac-va-mbp-work/default.nix

@@ -22,13 +22,14 @@ in
       };
 
       terminal = {
-        opencode = enabled;
+        aws = enabled;
         btop = enabled;
+        claude-code = enabled;
         direnv = enabled;
         git = enabled;
         k9s = enabled;
         nvim = enabled;
-        aws = enabled;
+        opencode = enabled;
       };
     };
   };
@@ -43,7 +44,9 @@ in
     texliveSmall # Pandoc PDF Dep
     google-cloud-sdk
     tldr
-    claude-code
+
+    # AI Assistants
     reichard.qwen-code
+    codex
   ];
 }

homes/x86_64-linux/evanreichard@lin-va-desktop/default.nix

@@ -0,0 +1,30 @@
+{ lib
+, config
+, namespace
+, ...
+}:
+let
+  inherit (lib.${namespace}) enabled;
+in
+{
+  home.stateVersion = "25.11";
+
+  reichard = {
+    user = {
+      enable = true;
+      inherit (config.snowfallorg.user) name;
+    };
+
+    services = {
+      ssh-agent = enabled;
+    };
+
+    programs = {
+      terminal = {
+        bash = enabled;
+        btop = enabled;
+        tmux = enabled;
+      };
+    };
+  };
+}

homes/x86_64-linux/evanreichard@lin-va-terminal/default.nix

@@ -22,12 +22,14 @@ in
     programs = {
       terminal = {
         bash = enabled;
-        tmux = enabled;
         btop = enabled;
+        claude-code = enabled;
         direnv = enabled;
         git = enabled;
         k9s = enabled;
         nvim = enabled;
+        opencode = enabled;
+        tmux = enabled;
       };
     };
   };