feat(TASK-033): add hook config schema across all scopes

Introduce src/hooks.rs as a types-only module (HookDef, HooksMap) and
plumb hooks:/global_hooks: config fields through every scope:

- Config + AppConfig hooks field, both Default impls, the manual
  from_config copy, and a COYOTE_HOOKS env override
- Role frontmatter: hand-parsed hooks arm, private field, getter, and
  JSON-inline re-serialization in Role::export (malformed maps degrade
  to None)
- AgentConfig + Graph: hooks + global_hooks on both structs, copied in
  AgentConfig::from_graph, with a per-agent global_hooks env override
- paths::hooks_dir() = <config_dir>/hooks with COYOTE_HOOKS_DIR override
- Commented hooks: block in the global config template (global scope
  only; no global_hooks key)

No engine or dispatch logic yet; existing configs parse unchanged.

src/hooks.rs

@@ -0,0 +1,12 @@
+use indexmap::IndexMap;
+use serde::{Deserialize, Serialize};
+
+/// A single named hook: an external command to run when its event fires.
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
+pub struct HookDef {
+    pub name: String,
+    pub command: String,
+}
+
+/// Ordered mapping of event name -> hook definitions, shared by every config scope.
+pub type HooksMap = IndexMap<String, Vec<HookDef>>;