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))

packages/lab-tool/utils/config.scm

@@ -135,7 +135,9 @@
           `((type . ,type)
             (hostname . ,hostname)
             (ssh-alias . ,ssh-alias)
-            (ssh-user . ,ssh-user)
+            (user . ,ssh-user)
+            (ssh-user . ,ssh-user)  ; Keep both for compatibility
+            (identity-file . "~/.ssh/id_ed25519_admin")  ; Default SSH key for sma user
             (is-local . ,(eq? type 'local))))
         #f)))