feat(TASK-049): add escalation.raised/answered, session.resumed, and agent.interrupted hook events

- escalation.raised fires in the child ctx after queue submit; escalation.answered
  fires in the parent ctx from the taken request, so both agree on origin envs
- escalation.* resolves global hooks ungated: the per-agent global_hooks whitelist
  never applies to these root-level events
- session.resumed fires on the use_session resume leg, inverse of session.started
- agent.interrupted replaces agent.completed/failed when the abort signal was
  ctrl-c'd: top-level bracket (now abort-aware), spawned-subagent result arm
  (agent__cancel / REPL ctrl-c), and graph agent nodes via the session signal;
  exit_agent and the shell-exit path stay non-interrupted by passing no signal
- document the deliberate non-fire paths (direct prompts, escalation timeout and
  parent-drop, graph approval nodes)

src/repl/mod.rs

@@ -533,7 +533,7 @@ Type ".help" for additional help.
         let exit_result = self.ctx.write().exit_session();
         self.ctx
             .write()
-            .top_level_agent_finished(exit_result.as_ref().err());
+            .top_level_agent_finished(exit_result.as_ref().err(), Some(&self.abort_signal));
         hooks::drain_pending(EXIT_HOOK_DRAIN_TIMEOUT).await;
         exit_result
     }