fix(cli): v0.5.7 — event loop keepalive for stdout flush

Node.js stdout to a pipe is buffered. Without periodic event loop
activity, WS callback → server.notification() → stdout.write() may
not flush until the next I/O event. A 1s setInterval (NOT unref'd)
keeps the event loop ticking so notifications flush immediately.

This is why claude-intercom worked: its 1s HTTP poll kept the event
loop active as a side effect. Claudemesh's passive WS listener let
the event loop settle, causing stdout to buffer indefinitely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/cli/src/ws/client.ts

@@ -526,8 +526,11 @@ export class BrokerClient {
       body: data,
       signal: AbortSignal.timeout(30_000),
     });
-    const body = await res.json() as { ok?: boolean; fileId?: string };
-    return body.fileId ?? null;
+    const body = await res.json() as { ok?: boolean; fileId?: string; error?: string };
+    if (!res.ok || !body.fileId) {
+      throw new Error(body.error ?? `HTTP ${res.status}`);
+    }
+    return body.fileId;
   }
 
   // --- Vectors ---