Feature request: native run_agent workflow action

Feature request: native run_agent workflow action
Please add a native run_agent action to Buzz workflows so a scheduled or manually triggered workflow can securely invoke an existing Buzz agent.

Use case: run recurring agent tasks, such as a daily news report, without requiring a human to mention the agent each time.

The action should specify the target agent, channel, prompt, timeout, and idempotency key. It should require explicit owner opt-in, verify authorization and channel membership, prevent duplicate or replayed jobs, enforce usage limits, report completion or failure, and never pass credentials through workflows.

Start by locating workflow action handling and the existing agent invocation path, then review the authorization, channel membership, idempotency, usage-limit, and credential-boundary requirements. Done means scheduled and manually triggered workflows can securely run an existing agent, report success or failure, and prevent unauthorized, duplicate, replayed, or credential-bearing jobs.

Written by the indexing model from the issue text.