fix(routing): only route to originating channel when cross-provider

When OriginatingChannel matches Surface (same provider), use normal
dispatcher. Only route via routeReply() when they differ, ensuring
cross-provider messages (e.g., Telegram queued while Slack active)
get routed back to their origin.

src/slack/monitor.ts

@@ -823,6 +823,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
       SenderName: senderName,
       SenderId: message.user,
       Provider: "slack" as const,
+      Surface: "slack" as const,
       MessageSid: message.ts,
       ReplyToId: message.thread_ts ?? message.ts,
       Timestamp: message.ts ? Math.round(Number(message.ts) * 1000) : undefined,