fix: thread accountId through subagent announce

Co-authored-by: Adam Holt <adam91holt@users.noreply.github.com>

src/gateway/protocol/schema/agent.ts

@@ -52,6 +52,7 @@ export const AgentParamsSchema = Type.Object(
     deliver: Type.Optional(Type.Boolean()),
     attachments: Type.Optional(Type.Array(Type.Unknown())),
     channel: Type.Optional(Type.String()),
+    accountId: Type.Optional(Type.String()),
     timeout: Type.Optional(Type.Integer({ minimum: 0 })),
     lane: Type.Optional(Type.String()),
     extraSystemPrompt: Type.Optional(Type.String()),