Start Setup From Picker

Skip-discovery entry point. The questionnaire path on /onboarding (and, later, the dashboard "Create new template" CTA) calls this to start a setup interview directly without going through a discovery call first.

Builds the same interview.context.prefill shape that the discovery-handoff webhook writes, so the specialist agent's PREFILL AWARENESS / recap behavior works identically regardless of entry path.

If surface == "embedded", attaches the "Embed Setup Handoff" skill at session-creation time. Other surfaces don't get the skill — they'll never hear MCP / API-key / coding-agent talk during setup.