fix(completion): offer unique hostnames without instance prefix

bash (and zsh without a matcher) only accept candidates that start with
the typed text, so "fsn1-bx1<Tab>" found nothing when every candidate
was qualified as "prod/…". Hostnames that exist in only one instance
are now offered bare; names present in several instances stay
qualified. Connecting to a bare name still checks every instance for
ambiguity, so the connection behavior is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/netssh/main.go

@@ -339,14 +339,13 @@ func rootCmd() *cobra.Command {
 			c := cache.New(cfg.CachePath(), cfg.Cache.TTL)
 			_ = c.Load()
 
-			hosts := c.Search(toComplete)
-			sort.Slice(hosts, func(i, j int) bool { return hosts[i].Name < hosts[j].Name })
+			hosts := hostCompletions(c.All(), toComplete)
 			if limit := cfg.Completion.MaxResults; limit > 0 && len(hosts) > limit {
 				hosts = hosts[:limit]
 			}
 			completions := make([]cobra.Completion, 0, len(hosts))
-			for _, e := range hosts {
-				completions = append(completions, cobra.Completion(e.Name))
+			for _, host := range hosts {
+				completions = append(completions, cobra.Completion(host))
 			}
 			// Subcommands at the end, after all hostnames.
 			for _, sub := range cmd.Commands() {