gateway: converge, don't start/stop/reload

The gateway is a deployment (castle-gateway) — its lifecycle is the same
convergence as everything else, so the bespoke start/stop/reload verbs
(which still routed through the retired enable/disable path) are gone.

- CLI: `castle gateway` is now inspection only — bare or `status` shows
  the route table. Start/stop/reload it via `castle apply` (render routes
  + reload) or `castle restart castle-gateway`. Deletes the last users of
  `_service_enable`/`_service_disable`, so those are removed too.
- API: retire `POST /gateway/reload` (making routes live is `POST /apply`);
  `PUT /gateway/config` message + docstring now say apply, not deploy.
- UI: GatewayPanel's "Reload" button → "Apply" (useApply); drop the
  useGatewayReload hook; GatewaySettings points at `castle apply`.
- docs: `castle gateway reload|status` → `castle gateway` (status lens).

core 129 / cli 31 / api 59 pass; dashboard builds clean; live `castle
gateway` shows routes with no start/stop/reload; /gateway/reload removed
from the API.

app/src/services/api/hooks.ts

@@ -226,16 +226,6 @@ export function useProgramAction() {
   })
 }
 
-export function useGatewayReload() {
-  const qc = useQueryClient()
-  return useMutation({
-    mutationFn: () => apiClient.post<{ status: string }>("/gateway/reload"),
-    onSuccess: () => {
-      qc.invalidateQueries({ queryKey: ["gateway"] })
-    },
-  })
-}
-
 export function useSaveGatewayConfig() {
   const qc = useQueryClient()
   return useMutation({