fix(daemon): accept string triggerPayload in workflow thread

The original code only accepted object-type triggerPayload, silently
discarding string values by replacing them with {}. This meant
`nerve workflow trigger <name> --payload '"some string"'` would
lose the payload entirely.

Changed to `triggerPayload ?? {}` so strings (and other non-null
values) pass through correctly.

小橘 🍊（NEKO Team）

packages/daemon/src/workflow-worker.ts

@@ -120,8 +120,7 @@ async function runThread(
 
   const initialEvent: CommandEvent = {
     type: "thread_start",
-    triggerPayload:
-      triggerPayload != null && typeof triggerPayload === "object" ? triggerPayload : {},
+    triggerPayload: triggerPayload ?? {},
   };
 
   // On resume: replay persisted events, run the next un-executed role, then continue.