feat(queue): immediate message persistence, streaming responses, and agent signatures (#256)

* feat(queue): stream responses via onEvent and add agent signature

Move response persistence and delivery into the onEvent progress
callback so responses are sent immediately as they arrive. Remove
duplicate post-invoke insert/send logic, keeping only an error
fallback. Append agent signature to direct responses.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs(skills): update skill-creator with eval and benchmarking workflow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jlia0