talent/chat: tighten report-back contract for talent_finished and talent_errored
When the latest trigger was talent_finished or talent_errored, the model sometimes redispatched the same task instead of producing an owner-facing report-back. Make the no-redispatch contract explicit in both the injected follow-up message and the trigger context block, and rewrite the chat-prompt rule line to be prescriptive.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>