feat: app-to-app integration framework + OnlyOffice handlers

Generic integration system for connecting deployed apps via toggle UI.
First handlers: OnlyOffice→FileBrowser (config.yaml patch) and
OnlyOffice→Nextcloud (occ CLI). Lifecycle hooks auto-suspend on
stop and re-apply on start.

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

controller/internal/stacks/manager.go

@@ -535,6 +535,12 @@ func deepCopyStack(s *Stack) Stack {
 		}
 	}
 
+	// Deep-copy Meta.Integrations
+	if s.Meta.Integrations != nil {
+		cp.Meta.Integrations = make([]IntegrationDef, len(s.Meta.Integrations))
+		copy(cp.Meta.Integrations, s.Meta.Integrations)
+	}
+
 	// Deep-copy Meta.HealthCheck pointer
 	if s.Meta.HealthCheck != nil {
 		hcCopy := *s.Meta.HealthCheck