Quick fixes from the first boot: recovery admin, upsell, warnings

- The recovery administrator (INBUXA_RECOVERY_ADMIN, or STALWART_RECOVERY_ADMIN)
  is honored only in bootstrap and recovery mode. On a configured server it's
  ignored with a startup warning. Before, it was a standing full-admin login
  for as long as the variable stayed set.
- The Enterprise upsell error is replaced by "This feature isn't available in
  INBUXA yet" for the features still to be rebuilt.
- Workspace warnings: 25 to 0. cargo fix removed the unused imports. The
  seven places where Enterprise code used to plug in keep their parameters,
  each with an inbuxa: comment naming the rebuild that uses it again. The
  antispam test's mock-server imports are back behind pending-rebuild.

crates/common/src/auth/permissions.rs

@@ -45,7 +45,8 @@ impl Server {
         &self,
         permissions: &structs::Permissions,
         role_ids: &[Id],
-        tenant_id: Option<u32>,
+        // inbuxa: unused until multi-tenancy is rebuilt: the tenant permission ceiling (docs/spec/features/multi-tenancy.md MT-13)
+        _tenant_id: Option<u32>,
     ) -> trc::Result<PermissionsGroup> {
         // Calculate effective permissions
         let (mut permissions, roles) = match permissions {