Preserve strict MCP auto-review outcomes (#40031)

## What changed

Propagate canonical denial, timeout, and abort responses from strict MCP
auto-review instead of replacing them with a generic decline. This preserves
the reviewer's action and metadata, including denial rationale, while still
failing closed when no canonical decision is available.

Update the fallback message to direct the agent to request explicit user
approval before proceeding.

## Testing

Add unit and app-server integration coverage for strict auto-review denials
and cancellations.

GitOrigin-RevId: d8126ab223ab546b95e2d984f6e4dd540a324a59

codex-rs/core/src/session/mcp.rs

@@ -807,7 +807,14 @@ async fn review_guardian_mcp_elicitation(
         )
         .await;
 
-        return Ok(matches!(decision, ReviewDecision::Approved).then(|| {
+        return Ok(matches!(
+            decision,
+            ReviewDecision::Approved
+                | ReviewDecision::Denied { .. }
+                | ReviewDecision::TimedOut
+                | ReviewDecision::Abort
+        )
+        .then(|| {
             mcp_elicitation_response_from_guardian_decision(decision, &turn_context.model_info)
         }));
     }