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/graph/executor.rs

@@ -928,6 +928,8 @@ mod tests {
             max_concurrent_agents: None,
             max_agent_depth: None,
             global_tools: Vec::new(),
+            hooks: Default::default(),
+            global_hooks: Vec::new(),
             mcp_servers: Vec::new(),
             mcp_tools: None,
             skills_enabled: None,