route(signals, fleet) -> RouteDecision via a deterministic cascade:
explicit host > capability-pin (uses hosts_with_capability) > sticky
(subject's session/task already runs on a host, via sessions+assignments)
> default-local. Pure + auditable (reason+candidates surfaced); the LLM
classify step and cross-host execution are separate layers. 13 tests.
Part of task 13764f2f.
(manual commit via ALLOW_COMMIT — autocommit LLM still down on claire)
