fix(traffic): show live Speed for AmneziaWG and MTProto inbounds/clients

The Speed column showed "--" for AmneziaWG (and MTProto, which has the
identical gap) even while cumulative traffic totals were correct.
XrayTrafficJob drives live speed by querying xray-core's own stats API
and broadcasting the delta over websocket -- but AmneziaWG/MTProto never
run inside xray-core's own runtime inbounds, so they're invisible to
that API. Their own jobs already compute the same per-poll delta shape
(that's what keeps cumulative totals correct) but never broadcast it.

Reusing the existing "traffics"/"clientTraffics" broadcast would have
two real bugs: the frontend's existing scope/replace logic would let
each side clobber the other's speed on its next unrelated tick, and the
websocket hub's per-message-type throttle is keyed only by message type,
not caller -- since both sidecar jobs run on identical "@every 10s"
grids registered milliseconds apart, one would silently lose almost
every broadcast if both protocols were ever configured together.

Fixed with a small unthrottled broadcast path (both sidecar jobs are
already self-rate-limited by their own cron cadence) and protocol-
namespaced wire keys, tracked in their own frontend state and merged
into the existing inboundSpeed/clientSpeed only at read time -- so every
existing consumer needs zero changes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/lib/traffic/poll-interval.ts

@@ -1 +1,5 @@
 export const TRAFFIC_POLL_INTERVAL_S = 5;
+
+// Mirrors cadenceAmneziaWG / cadenceMtproto in internal/web/web.go (both
+// "@every 10s"). If either cadence constant changes, update this to match.
+export const SIDECAR_TRAFFIC_POLL_INTERVAL_S = 10;