Guardian -> Auto-Review (#18021)

This PR is a user-facing change for our rebranding of guardian to
auto-review.

codex-rs/features/src/lib.rs

@@ -878,7 +878,7 @@ pub const FEATURES: &[FeatureSpec] = &[
         id: Feature::GuardianApproval,
         key: "guardian_approval",
         stage: Stage::Experimental {
-            name: "Guardian Approvals",
+            name: "Auto-review",
             menu_description: "When Codex needs approval for higher-risk actions (e.g. sandbox escapes or blocked network access), route eligible approval requests to a carefully-prompted security reviewer subagent rather than blocking the agent on your input. This can consume significantly more tokens because it runs a subagent on every approval request.",
             announcement: "",
         },

codex-rs/features/src/tests.rs

@@ -92,7 +92,7 @@ fn guardian_approval_is_experimental_and_user_toggleable() {
     let stage = spec.stage;
 
     assert!(matches!(stage, Stage::Experimental { .. }));
-    assert_eq!(stage.experimental_menu_name(), Some("Guardian Approvals"));
+    assert_eq!(stage.experimental_menu_name(), Some("Auto-review"));
     assert_eq!(
         stage.experimental_menu_description().map(str::to_owned),
         Some(