feat(lifecycle): runner + strategies + bus topic

Add decnet.lifecycle package: pure orchestration layer that the
master API will invoke via asyncio.create_task to drive DeckyLifecycle
rows through pending -> running -> succeeded | failed without
holding an HTTP request open.

Strategy classes per (operation, transport):
- LocalDeployStrategy: master-resident, runs engine.deployer.deploy
  in a thread.
- SwarmDeployStrategy: shards by host_uuid, dispatches via
  AgentClient.deploy; worker drives terminal via heartbeat.
- LocalMutateStrategy: write_compose + compose up.
- SwarmMutateStrategy: AgentClient.mutate; worker drives terminal.

decnet.bus.topics gains decky_lifecycle(name) -> decky.<name>.lifecycle
plus DECKY_LIFECYCLE constant. Payload documented in the wiki
(separate commit). publish_safely keeps bus best-effort.

Nothing is wired to call this yet -- next commits convert worker
/deploy /mutate to 202, then heartbeat delta wiring, then master API.

decnet/bus/topics.py

@@ -107,6 +107,11 @@ DECKY_SERVICE_REMOVED = "service_removed"
 # when the operator hit Apply (container was force-recreated to pick up
 # the new env), false when they only hit Save (DB-only).
 DECKY_SERVICE_CONFIG_CHANGED = "service_config_changed"
+# Async deploy/mutate operation transitions
+# (pending/running/succeeded/failed).  Payload: {lifecycle_id, operation,
+# status, error?}.  UI polling endpoint is the source of truth; this
+# fires for live subscribers (dashboard, mutator-side audit, etc).
+DECKY_LIFECYCLE = "lifecycle"
 
 # Attacker event types (second token under the ``attacker`` root).  First
 # sighting, session boundary transitions, and score-threshold crossings
@@ -391,6 +396,12 @@ def decky_mutation(decky_id: str) -> str:
     return f"{DECKY}.{decky_id}.{DECKY_MUTATION}"
 
 
+def decky_lifecycle(decky_id: str) -> str:
+    """Build ``decky.<id>.lifecycle``."""
+    _reject_tokens(decky_id)
+    return f"{DECKY}.{decky_id}.{DECKY_LIFECYCLE}"
+
+
 def system(event_type: str) -> str:
     """Build ``system.<event_type>``.