Remove steer feature flag (#12026)

All code should go in the direction that steer is enabled

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/features.rs

@@ -136,6 +136,7 @@ pub enum Feature {
     /// Emit skill approval test prompts/events.
     SkillApproval,
     /// Steer feature flag - when enabled, Enter submits immediately instead of queuing.
+    /// Kept for config backward compatibility; behavior is always steer-enabled.
     Steer,
     /// Allow request_user_input in Default collaboration mode.
     DefaultModeRequestUserInput,
@@ -638,7 +639,7 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::Steer,
         key: "steer",
-        stage: Stage::Stable,
+        stage: Stage::Removed,
         default_enabled: true,
     },
     FeatureSpec {