Adds the Stage 2 served ASK artifact adapter and adapter-only tests.
- Validates Q1-D DeliveredQuestion artifacts before ASK eligibility
- Uses ask_serving_enabled as a default-dark gate
- Uses the disclosure bus disposition mapping
- Fails closed to fallback surface/disposition on invalid artifacts
- Does not wire chat/runtime, telemetry, TurnEvent, ChatResponse, CLAIMS, or metrics
- Does not retire Q1B_ASK_CARVE_OUT or flip proposal_allowed
