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/graph/types.rs

@@ -588,6 +588,14 @@ nodes:
         ));
     }
 
+    #[test]
+    fn graph_silently_ignores_enabled_macros_key() {
+        let yaml = "name: g\nenabled_macros: [\"x\"]\nstart: x\nnodes:\n  x:\n    id: x\n    type: end\n    output: ok\n";
+        let graph: Graph = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(graph.name, "g");
+        assert_eq!(graph.start, "x");
+    }
+
     #[test]
     fn graph_settings_have_sensible_defaults() {
         let yaml = "name: g\nstart: x\nnodes:\n  x:\n    id: x\n    type: end\n    output: ok\n";