feat: deployed app removal + missing field injection (v0.19.0)

Add "Eltávolítás" to remove deployed (non-orphaned) stacks — reverts
them to "Nincs telepítve" while preserving templates for redeploy.
Modal offers HDD data and backup data cleanup choices.

Auto-inject missing deploy fields (secrets, domains) into existing
app.yaml when templates are updated via sync or on controller startup.

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

controller/internal/web/templates/stacks.html

@@ -76,6 +76,7 @@
                     <button class="btn btn-danger" onclick="stackAction(event, '{{.Name}}', 'stop')">Leállítás</button>
                 {{else}}
                     <button class="btn btn-success" onclick="stackAction(event, '{{.Name}}', 'start')">Indítás</button>
+                    {{if not .Orphaned}}<button class="btn btn-danger" onclick="removeStack('{{.Name}}')">Eltávolítás</button>{{end}}
                 {{end}}
                 <a href="/stacks/{{.Name}}/logs" class="btn btn-outline">Naplók</a>
                 {{if not .Orphaned}}<a href="{{appPageURL .Meta.Slug}}" class="btn btn-outline">Részletek</a>{{end}}