fix: resolve merge conflicts and fix threading tests

- Update MessageToolOptions type to include Slack threading options
- Remove duplicate threadTs property in slack/actions.ts
- Fix replyThreadTs parameter name in monitor.ts
- Update test to correctly verify 'first' mode threading behavior:
  - 'off' mode: no threading unless already in a thread
  - 'first' mode: first reply starts a thread
- Add new test case for 'first' mode threading

src/slack/monitor.ts

@@ -1110,7 +1110,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
             accountId: account.accountId,
             runtime,
             textLimit,
-            threadTs: effectiveThreadTs,
+            replyThreadTs: effectiveThreadTs,
           });
           hasRepliedRef.value = true;
         },