Add restricted AI worker access with deployment capabilities

- New module: modules/nixos/security/ai-worker-restricted.nix
  - Bind mount for infra repo access (RW)
  - Whitelisted sudo commands: nh, nixos-rebuild, nixpkgs-fmt, nix
  - Audit logging for infra changes
  - Documentation in README-ai-worker.md

- Updated users/ai-worker.nix:
  - Enable services.aiWorkerAccess
  - Lock password (SSH key only)
  - Security documentation comments

- Updated flake.nix:
  - Include new security module

SECURITY: AI must ask for user confirmation before running nh os switch

flake.nix

@@ -61,6 +61,7 @@
               ./modules/nixos/services/open_code_server.nix
               ./modules/nixos/services/ollama_init_custom_models.nix
               ./modules/nixos/services/openclaw_node.nix
+              ./modules/nixos/security/ai-worker-restricted.nix
               ./users/gortium.nix
               ./users/ai-worker.nix
             ];