fix: SFTP auto-refresh after file transfer

- Added program *tea.Program to SFTPBrowserTab and Model
- SetProgram() allows goroutines to send messages to Bubble Tea
- After transfer: program.Send(sftpRefreshMsg{}) triggers re-render
- Model stores program reference, passes to SFTP tab on creation

cmd/hostkeeper/tui.go

@@ -50,6 +50,7 @@ func runTUI(cmd *cobra.Command, args []string) error {
 	model.LoadHosts(hosts)
 
 	p := tea.NewProgram(model)
+	model.SetProgram(p)
 	if _, err := p.Run(); err != nil {
 		return fmt.Errorf("failed to run TUI: %w", err)
 	}