feat: support disabling bundled system skills (#13792)

Support disable bundled system skills with a config:

[skills.bundled]
enabled = false

codex-rs/core/src/config/config_tests.rs

@@ -1,6 +1,7 @@
 use crate::config::edit::ConfigEdit;
 use crate::config::edit::ConfigEditsBuilder;
 use crate::config::edit::apply_blocking;
+use crate::config::types::BundledSkillsConfig;
 use crate::config::types::FeedbackConfigToml;
 use crate::config::types::HistoryPersistence;
 use crate::config::types::McpServerTransportConfig;
@@ -155,6 +156,25 @@ consolidation_model = "gpt-5"
     );
 }
 
+#[test]
+fn parses_bundled_skills_config() {
+    let cfg: ConfigToml = toml::from_str(
+        r#"
+[skills.bundled]
+enabled = false
+"#,
+    )
+    .expect("TOML deserialization should succeed");
+
+    assert_eq!(
+        cfg.skills,
+        Some(SkillsConfig {
+            bundled: Some(BundledSkillsConfig { enabled: false }),
+            config: Vec::new(),
+        })
+    );
+}
+
 #[test]
 fn config_toml_deserializes_model_availability_nux() {
     let toml = r#"