feat(swarm): DeckyConfig.host_uuid + fix agent log/status field refs

- decnet.models.DeckyConfig grows an optional 'host_uuid' (the SwarmHost
  that runs this decky). Defaults to None so legacy unihost state files
  deserialize unchanged.
- decnet.agent.executor: replace non-existent config.name references
  with config.mode / config.interface in logs and status payload.
- tests/swarm/test_state_schema.py covers legacy-dict roundtrip, field
  default, and swarm-mode assignments.

decnet/models.py

@@ -99,6 +99,9 @@ class DeckyConfig(BaseModel):
     mutate_interval: int | None = None  # automatic rotation interval in minutes
     last_mutated: float = 0.0     # timestamp of last mutation
     last_login_attempt: float = 0.0 # timestamp of most recent interaction
+    # SWARM: the SwarmHost.uuid that runs this decky. None in unihost mode
+    # so existing state files deserialize unchanged.
+    host_uuid: str | None = None
 
     @field_validator("services")
     @classmethod