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

controller/internal/stacks/metadata.go

@@ -21,6 +21,7 @@ type Metadata struct {
 	AppInfo        AppInfo               `yaml:"app_info" json:"app_info"`
 	OptionalConfig []OptionalConfigGroup `yaml:"optional_config" json:"optional_config"`
 	HealthCheck    *HealthCheckConfig    `yaml:"healthcheck,omitempty" json:"healthcheck,omitempty"`
+	Integrations   []IntegrationDef     `yaml:"integrations,omitempty" json:"integrations,omitempty"`
 }
 
 // AppInfo holds detailed app information for the info page.
@@ -78,6 +79,13 @@ type SelectOption struct {
 	Label string `yaml:"label" json:"label"`
 }
 
+// IntegrationDef defines a single integration this app can provide to a target app.
+type IntegrationDef struct {
+	Target      string `yaml:"target" json:"target"`           // target app slug: "filebrowser", "nextcloud"
+	Label       string `yaml:"label" json:"label"`             // UI label (Hungarian)
+	Description string `yaml:"description" json:"description"` // UI description
+}
+
 // HealthCheckConfig defines controller-side health probe configuration.
 // When configured, the controller periodically probes the app's container
 // and overrides the stack state to "unhealthy" if the service is not responding.
@@ -210,3 +218,8 @@ func (m *Metadata) HasAppInfo() bool {
 func (m *Metadata) HasOptionalConfig() bool {
 	return len(m.OptionalConfig) > 0
 }
+
+// HasIntegrations returns true if the metadata defines any integrations.
+func (m *Metadata) HasIntegrations() bool {
+	return len(m.Integrations) > 0
+}