feat: add multi-host block support for SSH config management

- Support "Host server1 server2 server3" syntax in SSH configurations
- Add multi-host editing UI with separate host name inputs
- Implement multi-host block update and deletion operations
- Add comprehensive test coverage
- Maintain backward compatibility with single-host configs

internal/ui/update.go

@@ -394,9 +394,9 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			}
 		case ViewEdit:
 			if m.editForm != nil {
-				var newForm *editFormModel
-				newForm, cmd = m.editForm.Update(msg)
-				m.editForm = newForm
+				var updatedModel tea.Model
+				updatedModel, cmd = m.editForm.Update(msg)
+				m.editForm = updatedModel.(*editFormModel)
 				return m, cmd
 			}
 		case ViewMove: