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/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;
       };
     };
   };