feat: add enabled_macros config field at global, role, agent, and session levels

Mirrors the enabled_skills plumbing per plans/custom-commands-design.md §5:
- global: Config + AppConfig structs, from_config copy, and the
  COYOTE_ENABLED_MACROS env-override arm (csv_to_vec parsing)
- role: frontmatter via parse_string_or_array (list or csv string),
  plus the export() mirror so Role::save round-trips the field
- agent (non-graph): plain serde on AgentConfig; graph.yaml silently
  ignores the key (pinned by test, no field on Graph by design)
- session: plain serde with csv-or-vec deserializer

Empty list/string deserializes to Some([]) (explicit zero), distinct
from absent/null (None) — pinned by tests at every level, including
the env arm (serial-fenced against the from_config tests, which read
the process env via load_envs).

src/config/mod.rs

@@ -221,6 +221,8 @@ pub struct Config {
     #[serde(default, deserialize_with = "deserialize_csv_or_vec")]
     pub enabled_skills: Option<Vec<String>>,
     pub visible_skills: Option<Vec<String>>,
+    #[serde(default, deserialize_with = "deserialize_csv_or_vec")]
+    pub enabled_macros: Option<Vec<String>>,
 
     pub mcp_server_support: bool,
     pub mapping_mcp_servers: IndexMap<String, String>,
@@ -303,6 +305,7 @@ impl Default for Config {
             skills_enabled: true,
             enabled_skills: None,
             visible_skills: None,
+            enabled_macros: None,
 
             mcp_server_support: true,
             mapping_mcp_servers: Default::default(),
@@ -1124,6 +1127,42 @@ clients:
         assert!(cfg.enabled_mcp_servers.is_none());
     }
 
+    #[test]
+    fn config_enabled_macros_absent_is_none() {
+        let cfg: Config = serde_yaml::from_str("model: provider:test").unwrap();
+        assert_eq!(cfg.enabled_macros, None);
+    }
+
+    #[test]
+    fn config_enabled_macros_empty_string_is_some_empty() {
+        let cfg: Config = serde_yaml::from_str("enabled_macros: \"\"").unwrap();
+        assert_eq!(cfg.enabled_macros, Some(vec![]));
+    }
+
+    #[test]
+    fn config_enabled_macros_csv_string() {
+        let cfg: Config = serde_yaml::from_str("enabled_macros: \"a, b\"").unwrap();
+        assert_eq!(
+            cfg.enabled_macros,
+            Some(vec!["a".to_string(), "b".to_string()])
+        );
+    }
+
+    #[test]
+    fn config_enabled_macros_list() {
+        let cfg: Config = serde_yaml::from_str("enabled_macros:\n  - a\n  - b").unwrap();
+        assert_eq!(
+            cfg.enabled_macros,
+            Some(vec!["a".to_string(), "b".to_string()])
+        );
+    }
+
+    #[test]
+    fn config_enabled_macros_null_is_none() {
+        let cfg: Config = serde_yaml::from_str("enabled_macros: null").unwrap();
+        assert_eq!(cfg.enabled_macros, None);
+    }
+
     #[test]
     fn assert_state_pass_always_true() {
         let pass = AssertState::pass();