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
   ];
 }