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/scripts/plugins/llm_prompt.rs

@@ -4,9 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use sieve::{FunctionMap, compiler::Number, runtime::Variable};
-use std::time::Instant;
-use trc::{AiEvent, SecurityEvent};
+use sieve::{FunctionMap, runtime::Variable};
 
 use super::PluginContext;
 
@@ -14,7 +12,8 @@ pub fn register(plugin_id: u32, fnc_map: &mut FunctionMap) {
     fnc_map.set_external_function("llm_prompt", plugin_id, 3);
 }
 
-pub async fn exec(ctx: PluginContext<'_>) -> trc::Result<Variable> {
+// inbuxa: the LLM Sieve function is a no-op until AI classification is rebuilt
+pub async fn exec(_ctx: PluginContext<'_>) -> trc::Result<Variable> {
 
     Ok(false.into())
 }