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/web/server.go

@@ -15,6 +15,7 @@ import (
 	"gitea.dooplex.hu/admin/felhom-controller/internal/assets"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/integrations"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/monitor"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/notify"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/scheduler"
@@ -74,6 +75,9 @@ type Server struct {
 	// Asset syncer for Hub-managed assets (optional)
 	assetsSyncer *assets.Syncer
 
+	// App-to-app integration manager (optional)
+	integrationMgr *integrations.Manager
+
 	// Debug mode support
 	logBuffer      *LogBuffer
 	debugCallbacks *DebugCallbacks
@@ -163,6 +167,11 @@ func (s *Server) SetAssetsSyncer(as *assets.Syncer) {
 	s.assetsSyncer = as
 }
 
+// SetIntegrationManager sets the app-to-app integration manager.
+func (s *Server) SetIntegrationManager(mgr *integrations.Manager) {
+	s.integrationMgr = mgr
+}
+
 // SetLogBuffer sets the in-memory log ring buffer for the debug log viewer.
 func (s *Server) SetLogBuffer(lb *LogBuffer) {
 	s.logBuffer = lb