chore: re-put collab in experimental menu

codex-rs/core/src/features.rs

@@ -434,7 +434,11 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::Collab,
         key: "collab",
-        stage: Stage::Beta,
+        stage: Stage::Experimental {
+            name: "Multi-agents",
+            menu_description: "Allow Codex to spawn and collaborate with other agents on request (formerly named `collab`).",
+            announcement: "NEW! Codex can now spawn other agents and work with them to solve your problems. Enable in /experimental!",
+        },
         default_enabled: false,
     },
     FeatureSpec {