chore: remove skill metadata from command approval payloads (#15906)

## Why

This is effectively a follow-up to
[#15812](https://github.com/openai/codex/pull/15812). That change
removed the special skill-script exec path, but `skill_metadata` was
still being threaded through command-approval payloads even though the
approval flow no longer uses it to render prompts or resolve decisions.

Keeping it around added extra protocol, schema, and client surface area
without changing behavior.

Removing it keeps the command-approval contract smaller and avoids
carrying a dead field through app-server, TUI, and MCP boundaries.

## What changed

- removed `ExecApprovalRequestSkillMetadata` and the corresponding
`skillMetadata` field from core approval events and the v2 app-server
protocol
- removed the generated JSON and TypeScript schema output for that field
- updated app-server, MCP server, TUI, and TUI app-server approval
plumbing to stop forwarding the field
- cleaned up tests that previously constructed or asserted
`skillMetadata`

## Testing

- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-protocol`
- `cargo test -p codex-app-server-test-client`
- `cargo test -p codex-mcp-server`
- `just argument-comment-lint`

codex-rs/app-server/src/transport/mod.rs

@@ -379,7 +379,6 @@ pub(crate) async fn route_outgoing_envelope(
 mod tests {
     use super::*;
     use crate::error_code::OVERLOADED_ERROR_CODE;
-    use codex_app_server_protocol::CommandExecutionRequestApprovalSkillMetadata;
     use codex_app_server_protocol::ConfigWarningNotification;
     use codex_app_server_protocol::ServerNotification;
     use codex_utils_absolute_path::AbsolutePathBuf;
@@ -761,7 +760,7 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn command_execution_request_approval_strips_experimental_fields_without_capability() {
+    async fn command_execution_request_approval_strips_additional_permissions_without_capability() {
         let connection_id = ConnectionId(8);
         let (writer_tx, mut writer_rx) = mpsc::channel(1);
 
@@ -805,9 +804,6 @@ mod tests {
                                 macos: None,
                             },
                         ),
-                        skill_metadata: Some(CommandExecutionRequestApprovalSkillMetadata {
-                            path_to_skills_md: PathBuf::from("/tmp/SKILLS.md"),
-                        }),
                         proposed_execpolicy_amendment: None,
                         proposed_network_policy_amendments: None,
                         available_decisions: None,
@@ -824,11 +820,10 @@ mod tests {
             .expect("request should be delivered to the connection");
         let json = serde_json::to_value(message.message).expect("request should serialize");
         assert_eq!(json["params"].get("additionalPermissions"), None);
-        assert_eq!(json["params"].get("skillMetadata"), None);
     }
 
     #[tokio::test]
-    async fn command_execution_request_approval_keeps_experimental_fields_with_capability() {
+    async fn command_execution_request_approval_keeps_additional_permissions_with_capability() {
         let connection_id = ConnectionId(9);
         let (writer_tx, mut writer_rx) = mpsc::channel(1);
 
@@ -872,9 +867,6 @@ mod tests {
                                 macos: None,
                             },
                         ),
-                        skill_metadata: Some(CommandExecutionRequestApprovalSkillMetadata {
-                            path_to_skills_md: PathBuf::from("/tmp/SKILLS.md"),
-                        }),
                         proposed_execpolicy_amendment: None,
                         proposed_network_policy_amendments: None,
                         available_decisions: None,
@@ -897,17 +889,11 @@ mod tests {
                 "network": null,
                 "fileSystem": {
                     "read": [allowed_path],
-                    "write": null,
+                "write": null,
                 },
                 "macos": null,
             })
         );
-        assert_eq!(
-            json["params"]["skillMetadata"],
-            json!({
-                "pathToSkillsMd": "/tmp/SKILLS.md",
-            })
-        );
     }
 
     #[tokio::test]