fix: ensure consistent sma user for all SSH operations

- Add 'user' field mapping in get-ssh-config for compatibility
- Add default identity-file (~/.ssh/id_ed25519_admin) for sma user
- Fix update-flake function syntax error in deployment.scm
- All SSH operations (deploy, status, health, ssh command) now use sma user consistently

packages/lab-tool/lab/deployment.scm

@@ -63,5 +63,4 @@
 
 ;; Update flake inputs - delegate to ssh-deploy module  
 (define update-flake
-  "Update flake inputs (impure - has side effects)"
   (@ (lab ssh-deploy) update-flake))