fix: prevent attach/detach-server from repeating server arg on tab

Added __mcpctl_needs_server_arg guard in fish and position check in
bash so completions stop after one server name is selected.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

completions/mcpctl.bash

@@ -125,6 +125,8 @@ _mcpctl() {
       COMPREPLY=($(compgen -W "-i --input -p --password -c --conflict -h --help" -- "$cur"))
       return ;;
     attach-server)
+      # Only complete if no server arg given yet (first arg after subcmd)
+      if [[ $((cword - subcmd_pos)) -ne 1 ]]; then return; fi
       local proj names all_servers proj_servers
       proj=$(_mcpctl_get_project_value)
       if [[ -n "$proj" ]]; then
@@ -137,6 +139,8 @@ _mcpctl() {
       COMPREPLY=($(compgen -W "$names" -- "$cur"))
       return ;;
     detach-server)
+      # Only complete if no server arg given yet (first arg after subcmd)
+      if [[ $((cword - subcmd_pos)) -ne 1 ]]; then return; fi
       local proj names
       proj=$(_mcpctl_get_project_value)
       if [[ -n "$proj" ]]; then