Pi Workflows 0.16.6

Pi Workflows 0.16.6 fixes workflow response routing and strengthens durable execution.

• Agent submit and update operations now target the exact durable request.
• Invalid or mismatched responses are rejected before any workflow state changes.
• Controls now follow the actual pending response type instead of the broad waiting status.
• Checkpoints complete in their original run instead of creating a continuation child.
• Queue scheduling, response receipts, follow-ups, terminal capture, pause timing, and execution-revision recovery now use one checked durable execution path.

This fixes the case where answer could be accepted for an agent step, create an invalid continuation, and leave the real agent request pending. The SQLite schema remains version 1 and follows the existing alpha hard-cut policy.