feat(communication): federate tenant collaboration with signed delivery

.env.example

@@ -51,6 +51,11 @@ SEAFILE_ADMIN_PASSWORD=change-this-seafile-admin-password
 
 M2M_API_KEY=change-this-m2m-key
 API_BASE_URL=https://app.example.com/backend
+# Collaboration: public browser URL and canonical HTTPS API address (including reverse-proxy prefix).
+FEDEO_PUBLIC_URL=https://app.example.com
+FEDEO_FEDERATION_URL=https://app.example.com/backend
+# Requires mutual tenant partner approval under Zusammenarbeit.
+FEDEO_FEDERATION_ENABLED=false
 GOCARDLESS_BASE_URL=https://api.gocardless.com
 GOCARDLESS_SECRET_ID=replace-this
 GOCARDLESS_SECRET_KEY=replace-this