An action on a name that is no app answers 404, not 'settings cannot be saved' (found walking capability map B2 on 9202)

Test TestAnActionOnANameThatIsNoAppIsA404 red first. Commit only.

controller/internal/stacks/desiredstate.go

@@ -3,6 +3,8 @@ package stacks
 import (
 	"fmt"
 	"path/filepath"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/util"
 )
 
 // Desired-state values for AppConfig.DesiredState (R-166, decision D-b).
@@ -57,7 +59,8 @@ func (m *Manager) SetDesiredState(name, desired string) error {
 
 	stack, ok := m.GetStack(name)
 	if !ok {
-		return fmt.Errorf("stack %q not found", name)
+		// a KIND (404 at the API) and the household's sentence — not a save failure
+		return util.MsgErrorf(ErrStackNotFound, "err.stacks.alkalmazas_nem_talalhato", name)
 	}
 	stackDir := filepath.Dir(stack.ComposePath)