fix(slack): respect verbose setting and preserve thread context for tool notifications

Fixes two bugs in Slack tool notification delivery:

1. Tool notifications ignored verbose=false - normalized verbose values so
   boolean false/'false' are properly treated as 'off'

2. Thread context lost - Slack outbound adapter now falls back to threadId
   when replyToId is missing, and MessageThreadId is set for thread replies

Closes #1333

src/slack/monitor/message-handler/prepare.ts

@@ -476,6 +476,8 @@ export async function prepareSlackMessage(params: {
     Surface: "slack" as const,
     MessageSid: message.ts,
     ReplyToId: message.thread_ts ?? message.ts,
+    // Preserve thread context for routed tool notifications (thread replies only).
+    MessageThreadId: isThreadReply ? threadTs : undefined,
     ParentSessionKey: threadKeys.parentSessionKey,
     ThreadStarterBody: threadStarterBody,
     ThreadLabel: threadLabel,