feat(swarm): heartbeat-driven topology resync for agent-pinned deployments

Agent heartbeats now carry an applied-topology snapshot. The master
heartbeat handler compares the reported version_hash against what
canonical_hash yields for the hydrated topology pinned to that host
and flags Topology.needs_resync on divergence (or when the agent
reports no topology at all while master expects one).

The mutator watch loop gains reconcile_agent_resyncs, which re-pushes
the current hydrated blob via AgentClient.apply_topology without
touching status, then clears the flag on success. Push failures leave
the flag set so the next tick retries.

decnet/web/db/repository.py

@@ -268,6 +268,12 @@ class BaseRepository(ABC):
     async def delete_topology_cascade(self, topology_id: str) -> bool:
         raise NotImplementedError
 
+    async def set_topology_resync(self, topology_id: str, value: bool) -> None:
+        raise NotImplementedError
+
+    async def list_topologies_needing_resync(self) -> list[dict[str, Any]]:
+        raise NotImplementedError
+
     async def add_lan(self, data: dict[str, Any]) -> str:
         raise NotImplementedError