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/handlers.go

@@ -478,6 +478,12 @@ func (s *Server) appDetailHandler(w http.ResponseWriter, r *http.Request, slug s
 	data["HasOptionalConfig"] = found.Meta.HasOptionalConfig()
 	data["EffectiveSubdomain"] = effectiveSubdomain
 
+	// App-to-app integrations
+	if found.Meta.HasIntegrations() && s.integrationMgr != nil {
+		data["HasIntegrations"] = true
+		data["Integrations"] = s.integrationMgr.ListForProvider(found.Meta.Slug)
+	}
+
 	// Geo-restriction per-app data
 	geo := s.settings.GetGeoRestriction()
 	if geo != nil && geo.Enabled && s.cfg.Infrastructure.CFAPIToken != "" {
@@ -1615,6 +1621,10 @@ func (s *Server) SyncFileBrowserMounts() {
 		s.logger.Printf("[ERROR] Failed to recreate FileBrowser: %s — %v", string(out), err)
 	} else {
 		s.logger.Printf("[INFO] FileBrowser mounts synced — %d storage path(s), config updated", len(paths))
+		// Re-apply active integrations (config regeneration overwrites config.yaml)
+		if s.integrationMgr != nil {
+			go s.integrationMgr.OnStackStart(context.Background(), "filebrowser")
+		}
 	}
 }