Adds a fleet_singletons array to ServiceCatalogResponse so per-decky
add UIs can filter out services like LLMNR that run once fleet-wide
(and would 422 server-side at the live add endpoint).
The existing 'services: list[str]' field is unchanged for back-compat
with MazeNET/useMazeApi.ts:257; the new field is additive.
decnet_web/src/hooks/useServiceRegistry.ts wraps the endpoint with a
module-scoped cache (registry only changes on BYOS install / plugin
drop, neither of which happens mid-session) and exposes a precomputed
.perDecky list so consumers don't need to re-derive the diff.
anti
06f208c86e