fix(dashboard): bind editMessage to channel to stop repost loop

The retry refactor captured `const editMessage = channel.editMessage` and
called it detached, losing `this`. Every status edit then threw
"this.client is undefined", so each cycle failed all retries and reposted a
fresh (notifying) status message — ~50 reposts in 30 minutes. Bind the method
to the channel so the edit runs in place. Adds a regression test showing a
detached method fails while a bound one succeeds.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/unified-dashboard.ts

@@ -916,7 +916,10 @@ export async function startUnifiedDashboard(
         // immediately spawn a fresh status message. Retry the edit a couple of
         // times with a delay first; only give up (and repost) if all fail.
         const editId = statusMessageId;
-        const editMessage = channel.editMessage;
+        // Bind to the channel: a detached method reference loses `this` and the
+        // edit throws ("this.client is undefined"), which would make every
+        // update fail and repost a fresh (notifying) message.
+        const editMessage = channel.editMessage.bind(channel);
         // First render after start: 0 retries → repost immediately if the edit
         // fails. Steady state: retry twice at 15s before reposting.
         const maxRetries = firstStatusRender ? 0 : STATUS_EDIT_MAX_RETRIES;