fix(issue-18): bind the heartbeat timer to the agent process; scope started to the attempt; ignore re-sent finished dispatches

Review round 1 (claude NOT PASS) corrections:
- B2: the timer now watches a process - `--watch-pid`, or by default the
  nearest agent-CLI ancestor of the publishing command - and stops within
  one period once it is gone, so a crashed agent stops heartbeating and is
  closed after K x N; a remote runner watches itself. Documented as process
  liveness (an alive-but-stuck agent keeps heartbeating).
- R1: `_wait_started` accepts an events.log `started` only when it carries
  the current dispatch token (loop jobs share one events.log).
- R2: the remote runner ignores a re-sent dispatch of an attempt that
  already reached its terminal.
- R3: registry.md EOF blank line (git diff --check clean).
- R4: the ack error states the effective budget when the wall clock cut it.
- P3: stop_timer verifies the pidfile pid is this job's timer before
  signalling; a retained state message keeps its own seq watermark so it
  can never make the monotonic guard drop its own event.
- MULTI_AGENT_RULES.md timeout section updated for the contract.
- tests: agent-process death stops the timer, recycled-pid safety,
  attempt-scoped started, re-sent dispatch; acceptance 3 now kills the
  agent process instead of the timer. Help captures refreshed
  (--watch-pid). The wrapper can be sourced with
  MAM_DELEGATE_JOB_NO_MAIN=1 for helper-level tests.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/fixtures/issue_5/phase1/help-publish_event.txt

@@ -7,7 +7,8 @@ usage: publish_event.py [-h] (--job JOB | --pick-pending)
                         [--side-effect KIND=REFERENCE]
                         [--attempt-id ATTEMPT_ID]
                         [--expect-dispatch-token EXPECT_DISPATCH_TOKEN]
-                        [--heartbeat N] [--no-state] [-v]
+                        [--heartbeat N] [--no-state] [--watch-pid WATCH_PID]
+                        [-v]
 
 Publish a Job event to MQTT
 
@@ -39,4 +40,7 @@ optional arguments:
                         the job ends (Issue #18; not with a terminal event)
   --no-state            do not publish the retained <topic_prefix>/state
                         message
+  --watch-pid WATCH_PID
+                        bind the heartbeat timer to this process (default: the
+                        nearest agent-CLI ancestor; 0 = no watch)
   -v, --verbose