Require automatic review for high-risk Guardian v2 actions (#38569)

## What changed

- Add a thread-scoped extension API for requesting automatic review, resolving
  multiple contributors to the strongest requirement.
- Have Guardian v2 request automatic review when it is enabled and the latest
  `action_risk` score is at least `0.8`.
- Honor extension review requirements across tool approvals, MCP elicitation,
  and remote execution while preserving host configuration and managed-policy
  constraints.

## Testing

- Cover contributor registration and requirement resolution.
- Verify Guardian v2 requests review at the threshold, returns to the default
  below it, and does not affect threads where the extension is disabled.
- Exercise extension-requested strict review with a remote model override.

GitOrigin-RevId: 6329fc23585d5cc7173c39bb9952c3109ec3884b

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

@@ -833,7 +833,9 @@ async fn review_guardian_mcp_elicitation(
         request.server_name.as_str(),
         elicitation_connector_id(&request.elicitation),
     );
-    if !crate::guardian::routes_approval_policy_to_guardian(approval_policy, approvals_reviewer) {
+    if !crate::guardian::routes_approval_policy_to_guardian(approval_policy, approvals_reviewer)
+        && !session.extension_strict_auto_review_enabled().await
+    {
         return Ok(None);
     }