fix(issue-18): default ack timeout T = 180 s

In the v4.5.0 review round grok read the brief and published `started`
70 s after the injection; with T = 60 the wrapper had already closed the
job as agent_blocked and refused its later PASS. T bounds delivery, not
work, so a generous default costs nothing when the agent answers fast.
Code, docs and the CLI snapshot updated together.

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

tests/test_issue5_phase1_delegation.py

@@ -343,7 +343,7 @@ def test_registry_cli_contract_snapshot(mam_sandbox):
     assert reg["--idle-timeout"][2] is None
     assert reg["--heartbeat-sec"][2] == 30
     assert reg["--heartbeat-misses"][2] == 4
-    assert reg["--ack-timeout"][2] == 60
+    assert reg["--ack-timeout"][2] == 180
     assert reg["--transport"][1] == ("herdr", "remote")
     assert registry.liveness_window(reg["--heartbeat-sec"][2], reg["--heartbeat-misses"][2]) == 120
     assert reg["--bits"][2] == 32