feat: Add little-rascal laptop config and lab-tool auto-update system

## New Machine: little-rascal
- Add Lenovo Yoga Slim 7 14ARE05 configuration (AMD Ryzen 7 4700U)
- Niri desktop with CLI login (greetd + tuigreet)
- zram swap configuration (25% of RAM with zstd)
- AMD-optimized hardware support and power management
- Based on congenital-optimist structure with laptop-specific additions

## Lab Tool Auto-Update System
- Implement Guile Scheme auto-update module (lab/auto-update.scm)
- Add health checks, logging, and safety features
- Integrate with existing deployment and machine management
- Update main CLI with auto-update and auto-update-status commands
- Create NixOS service module for automated updates
- Document complete implementation in simple-auto-update-plan.md

## MCP Integration
- Configure Task Master AI and Context7 MCP servers
- Set up local Ollama integration for AI processing
- Add proper environment configuration for existing models

## Infrastructure Updates
- Add little-rascal to flake.nix with deploy-rs support
- Fix common user configuration issues
- Create missing emacs.nix module
- Update package integrations

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

modules/users/common.nix

@@ -29,12 +29,7 @@
       eval "$(direnv hook zsh)"
     '';
 
-    # Common environment variables
-    sessionVariables = {
-      EDITOR = "emacs";
-      BROWSER = "firefox";
-      TERMINAL = "kitty";
-    };
+    # Removed sessionVariables - moved to environment.sessionVariables
   };
 
   # Common packages for all users