Add skill approval event/response (#12633)

Set the stage for skill-level permission approval in addition to
command-level.

Behind a feature flag.

codex-rs/core/src/features.rs

@@ -131,6 +131,8 @@ pub enum Feature {
     SkillMcpDependencyInstall,
     /// Prompt for missing skill env var dependencies.
     SkillEnvVarDependencyPrompt,
+    /// Emit skill approval test prompts/events.
+    SkillApproval,
     /// Steer feature flag - when enabled, Enter submits immediately instead of queuing.
     Steer,
     /// Enable collaboration modes (Plan, Default).
@@ -611,6 +613,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::SkillApproval,
+        key: "skill_approval",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::Steer,
         key: "steer",