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/protocol/src/skill_approval.rs

@@ -0,0 +1,15 @@
+use schemars::JsonSchema;
+use serde::Deserialize;
+use serde::Serialize;
+use ts_rs::TS;
+
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, Eq, JsonSchema, TS)]
+pub struct SkillRequestApprovalEvent {
+    pub item_id: String,
+    pub skill_name: String,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, Eq, JsonSchema, TS)]
+pub struct SkillApprovalResponse {
+    pub approved: bool,
+}