fix(slack): pass threadId param in message read action

The Slack channel plugin's read action handler was not forwarding the threadId parameter to handleSlackAction, causing message action=read channel=slack threadId=X to always return channel history instead of thread replies.

extensions/slack/src/channel.ts

@@ -337,6 +337,7 @@ export const slackPlugin: ChannelPlugin<ResolvedSlackAccount> = {
             limit,
             before: readStringParam(params, "before"),
             after: readStringParam(params, "after"),
+            threadId: readStringParam(params, "threadId"),
             accountId: accountId ?? undefined,
           },
           cfg,