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/app-server-protocol/src/protocol/common.rs

@@ -671,6 +671,11 @@ server_request_definitions! {
         response: v2::ToolRequestUserInputResponse,
     },
 
+    SkillRequestApproval => "skill/requestApproval" {
+        params: v2::SkillRequestApprovalParams,
+        response: v2::SkillRequestApprovalResponse,
+    },
+
     /// Execute a dynamic tool call on the client.
     DynamicToolCall => "item/tool/call" {
         params: v2::DynamicToolCallParams,