feat: ground venue booking answers in Events booking guides

[chubes4]

Need

Extra Chill Events PR Extra-Chill/extrachill-events#531 adds the venue-owned booking-guide contract required by Extra-Chill/extrachill-events#526. Roadie now needs focused consumer wiring so artists and venue operators receive grounded answers rather than inferred venue facts.

Related booking operator work: #88 and PR #102.

Events contract

Call extrachill/get-venue-booking-guide through the existing caller-bound Events adapter with the exact pinned venue_term_id.

The response contains only:

• venue_term_id
• venue_name
• config_revision
• guide_version
• ordered entries with key, title, body, and visibility (public or operator)

Events permission checks require exact active venue membership. The narrow response excludes correspondence addresses, deal defaults, ticket provider references, and unrelated booking config.

Acceptance

• Add a bounded Roadie read/answer path that delegates to extrachill/get-venue-booking-guide as the bound human user.
• Materialized venue Roadies remain pinned to their exact venue; cross-venue reads fail closed.
• Answers use only returned guide entry content and identify unavailable answers honestly rather than filling gaps from model knowledge.
• Include the returned venue identity and current config revision in answer context/citations.
• Respect entry visibility for the calling surface. Do not expose operator entries through public tools, public prompts, logs, or markup.
• Do not duplicate guide content in Roadie source, prompts, defaults, or fixtures beyond contract-shaped test data.
• Keep unknown questions in the managed booking inquiry/thread flow; do not expose personal coordinator details.
• Test empty guides, unavailable topics, stale/current revision context, visibility filtering, caller binding, and cross-venue denial.

Dependency

Implement after or against Events PR Extra-Chill/extrachill-events#531. Do not merge/release/deploy as part of this issue without normal review.